A Short Introduction to the Maple Language

This section contains an introduction to some of the Maple vocabulary used for solving problems. It is not meant to cover everything, just some of the basics. Read it through quickly, to get an overview of the language. Then you can come back and read with more understanding later.

Arithmetic

First, there is arithmetic: addition, subtraction, multiplication, division and exponentiation. These can be combined, just as on a calculator. The order of precedence is the the usual one: exponentiation first, then multiplication and division, then addition and subtraction. So saying (that is, typing in and pressing the enter key)

> 2-3+4/5*6^7;

is the same as saying

> (2-3)+(4/5)*(6^7);

You will notice that Maple works with fractions whenever possible, changing to decimal numbers only on demand. So typing and entering (pressing the enter key)

> 1/3 + 1/2;

will get a return of 5/6. If you put a decimal point in one of the numbers, that forces Maple to return a decimal answer.

> 1/3. + 1/2;

> evalf(1/2+1/3);

The Maple constant Digits is set to 10 by default. If you want to more or less digits of accuracy, use evalf with a second argument.

> Pi*3^2;

Maple leaves in its symbolic form unless instructed to convert to floating point. For example, if we wanted the area of our circle to 100 digits of accuracy, we could say

> evalf(Pi*3^2,30);

>

>

This command returned the value of to rounded to 30 digits of accuracy. If you want all of your floating point caluculation to be done with 30 digits of accuracy, set Digits to 30;

> Digits :=30;

> sqrt(2) + sqrt(3) = sqrt(2.) + sqrt(13.);

>

I usually don't mess with Digits unless I am investigating the accuracy of some numerical method.

> Digits := 10;

Maple does arithmetic with complex numbers too. I is a Maple constant standing for . So entering

> (3+2*I)*(2-I)/(3-I);

>

will produce an output of .

To get the principal square root of 2+I, say

> sqrt(2+I);

To express it in the form , use evalc

> sqrt(2+I)=evalc(sqrt(2+I));

Complex numbers first come up when you solve quadratic equations.

>

> solve(3*x^2+2*x +1 ,x);

>

Expressions, Names, Statements, and Assignments

name := expression; For example, the assignment

> area := Pi*3^2;

stores in a location marked by the name area.

A more useful assignment for the area of a circle is

> area := Pi*r^2;

> subs(r=3,area);

Here, it is convenient to think of the assignment as defining area as a function of the radius r.

Functions

Functions can be defined in several useful ways in Maple.

As an expression: The assignment

> area := Pi*r^2;

defines the area of a circle as a function of it's radius. The area function defined as an expression is evaluated with subs. Since this function assigns real numbers to real numbers, its values can be plotted on a graph with the Maple word plot. So the statement

> plot(area,r=0..4);

will produce in a separate plot window, the graph of the area function over the interval from to .

> area := r -> Pi*r^2;

defines the area function also. Now to find the area of a circle of radius 3, we simply enter the statement

> area(3);

To plot this function over the domain r = 0..4 , say

> plot(area,0..4);

Note that the variable r is omitted here.

> pol := x^2 + 4*x -1;

then the assignment

> pol := unapply(pol,x);

turns pol into a function defined by an arrow operator.

> area := proc(r) Pi*r^2 end;

> area := proc(r)

> if r <= 0 then ERROR("radius must be positive") else

> Pi*r^2 fi end;

> area(3);

> area(-3);

Error, (in area) radius must be positive

Functions of two variables can be defined and plotted just as easily in Maple as functions of one variable. For example, the volume V of a cylinder of height h and radius r is defined by

> V := (r,h) -> Pi*r^2*h;

> plot3d(V,0..4,0..4,axes=boxed);

Which way of defining a function is the preferred way? That really depends on the situation. The expression method works well for functions which have only one rule of evaluation, but eventually you cannot avoid using an -> or proc definition. You will find yourself using arrow or proc definitions more and more as time goes by.

Piecewise defined functions:

> f :=unapply(piecewise(x <= -1,x^3+8, x <= 2,7+ 2*x, x <= 4, 11 - cos(x),3*x),x);

> f(2);

When plotting piecewise defined functions, sometimes style = point is better.

> plot(f, -3..6,style= point);

You can also plot discontinuous functions by setting discont = true.

> plot(f, -3..6,discont=true,color=blue);

>

>

Composition of functions

One of the important skills needed for calculus and other mathematics is the skill to see a function as built up from simpler functions by the 4 arithmetic operations plus composition. In Maple these operations are named by +, *, -, /, and @. So for example the function can be seen as the quotient of g (x) = by h(x) = .

>

> g := x-> x^2 +1; h := x->sqrt(x^3-1);

> f := g/h;

> f(x);

This analysis of a function into simpler functions is not unique and can often be extended further. For example, the denominator function h is seen to be the composition of the square root function with the cubic polynomial function .

> k := x-> x^3 -1;

> f := g/ (sqrt @ k) ;

> f(x);

Problem: Define three functions g,h, and k so that the function f defined by is

Built in Maple functions and Operations with Functions

> ?inifcns;

> y := sin(cos(x^2+3));

and evaluated at x=3 by

> subs(x=3.,y);

could also be defined by the assignment

> y := sin@cos@(x->x^2+3);

and evaluated at x=3 by

> y(3.);

Using Maple as a fancy graphing calculator.

It is convenient to think of Maple as a fancy graphing calculator for many purposes. For example, suppose you want to find the real solutions of the equation in the interval . Then we can just plot the right hand side of the equation and look for where the graph crosses the x-axis.

> f := x -> 10*x^5 - 30*x +10 ;

> plot(f,-3..3);

By inspection, the graph crosses near 0. We can look closer.

> plot(f,-1.5..1.5);

>

> fsolve(f(x)=0,x,1..1.5);

Data types, Expression Sequences, Lists, Sets, Arrays, Tables

> whattype(1/2);

> whattype(a + b);

> whattype(x^2 + x = 2*x - 1);

> whattype(a,b,3);

Expression Sequence.

> viola := 1,2, w*r+m, a=b+c, 1/2, (x+y)/z,`hello`;

is an assignment to viola of an expression sequence of 7 expressions. To refer to the sixth expression in this sequence, use the expression viola[6];

> viola[6];

List .

> explist:= [viola];

makes a list whose terms are those in viola . As with expression sequences, we can refer to particular terms of a list by appending to its name the number of the term enclosed in square brackets. Thus to get the fifth term of explist , type the expression

> explist[3];

> op(3,explist);

In general, op(n,explist); returns the nth term in the list explist .

> nops(explist);

tells us that there are 7 terms in the list explist . nops comes in handy when you

don't want to (or aren't able to) count the terms in a list by hand.

You can't directly use the word nops to count the number of terms in an expression sequence. But you can put square brackets around the expression sequence and count the terms in the resulting list. This device is used again and again.

> nops(3,4,a);

Error, wrong number (or type) of parameters in function nops

> nops([3,4,a]);

> p := [1,2]; q := [-3,1];

> w := 3*p + 2*q - p;

One important use of lists is to make lists of points to plot. For example, to draw a picture of the square with vertices (1,1), (3,1), (3,3), (1,3), make a list and then plot it.

> ab := [[1,1],[3,1],[3,3],[1,3],[1,1]];

> plot(ab);

Notice in the graph that the origin is not included in the field of view. We can specify that by restricting the x and y coordinates.

> plot(ab,x=0..4,y=0..4);

> plot([1+4*cos(t),5+4*sin(t),t=0..Pi],
scaling=constrained);

If you had to draw several pieces of circles, you might define a function to simplify things. You can call the function whatever you want, say circ.

> circ := (h,k,r,f,l) -> [h+r*cos(t),k+r*sin(t),t=f..l];

So if we wanted circles of radius 1/2 centered at the corners of the square ab we can construct the sequence of lists. Here is where the Maple word seq comes in handy.

> circs := seq(circ(op(ab[i]), 1/2,0,2*Pi),i=1..4);

In order to plot these circles, you need to enclose them in curly brackets to make a set of the sequence before you give them to plot . See below for a discussion of sets.

> plot({circs,ab},scaling=constrained);

> xdat := [ seq(ab[i][1],i=1..nops(ab) )];

> ydat := [seq(ab[i][2],i=1..nops(ab) )];

What about the converse problem? Building up a list of points to plot from two lists can also be done. The first thing you might think of doesn't work, however.

> seq([xdat[i],ydat[i]],i=1..nops(xdat));

Seq doesn't work well with a pure expression sequence as input. However, with some coaxing we can get it to do what we want.

> newab :=[seq([xdat[i],ydat[i]],i=1..nops(xdat))];

What did we do to change the input to seq ? We enclosed it in square brackets. If you feed such a list of points to plot, it knows what to do. If you wanted to strip out the inside brackets, that can be done too, but in release 4 of Maple, plot would treat it as a sequence of constant functions.

> newab := [seq(op([xdat[i],ydat[i]]),i=1..nops(xdat))];

> plot(newab,color=black);

>

Sets

> Aset := {y+x+1,1,2,1,4,`bill`,x+y+1,`bill`};

> Anotherset := Aset union {4,3,a,7} ;

> Anotherset minus Aset, Anotherset intersect Aset;

Sets are important when plotting more than one function at at time, to plot the quadratic function and the linear function on the same axes,

> plot({x^2-2,2*x+5},x=-5..5);

>

> pl1 := plot({x^2-2,2*x+5},x=-5..5):

> pl2 := plot([[2,1],[3,20],[0,0],[2,1]]):

> plots[display]([pl1,pl2]);

>

Tables and Arrays

> a := array(1..2,1..2);

>

creates a 2 by 2 matrix, whose entries are accessed as a[1,1] etc.

So to rotate the square through an angle of 31 degrees counter clockwise about the origin and display it, we could proceed as follows.

> rot := array([[cos,-sin],[sin,cos]]);

> ang := evalf(Pi/180*31);

> ab := [[1,1],[3,1],[3,3],[1,3],[1,1]];

> rotab := [seq(convert( evalm(rot(ang)&*ab[i]),list) ,i=1..nops(ab) )];

> plot({ [[0,0]],ab,rotab} );

Maple control statements

There are two especially important control statements . One is the repetition loop , and the other is the conditional execution statement. The repetition loop is

for .. from .. by .. to .. while .. do .. od

and the conditional execution statement is

if ... then ... elif ... else ... fi

These statements can be used interactively or in a procedure.

Example: Add up the first 10000 numbers.

> s := 0: for i from 1 to 10000 do s := s+i od: s;

Note: The Maple word sum could be used here instead.

> i := 'i': sum(i,i=1..10000);

> i;

Note: This could also be computed using convert and seq .

> convert([seq(i,i=1..10000)],`+`);

Example: Add up the odd numbers between 1 and 973.

> s := 0: for i from 1 by 2 to 973 do s := s + i od: s;

Example: Add up the prime numbers between 1 and 10000

> s := 0: for i from 1 to 10000 do if isprime(i) then s := s+i fi od: s;

Example: Add up the first 1000 primes.

> s := 0: j := 0: for i from 1 by 2 while j <1000 do if isprime(i) then
s := s+i; j:= j+1 fi od: s;

>

Example: Compute the cubes of the first five positive integers and store them in a list. Then do it again, storing them in an array.

Solution with lists:

for i from 1 to 5 do
locube := locube ,i^3 od:
locube := [locube]; # make locube a list.;

> locube[3]:=15;

> locube;

Note the way the list is built up from an empty exprseq NULL . Each time through the loop, one more term is added onto the end of the sequence. At the end, square brackets are put around the sequence, making it a list. With arrays, one can be more direct.

Solution with arrays:

> aocube := array(1..5): # initialize the array.

> for i from 1 to 5 do aocube[i]:= i^3 od;

> op(aocube); # to see the array

>

Now the array aocube has the numbers stored in it. To refer to the third element of aocube , we would enter aocube[3] just as if it were a list, rather than an array.

> aocube[3]:=0;

> print(aocube);

> locube := [locube[1],locube[2],0,locube[4],locube[5]];

>

Conditional execution

if .. then .. elif .. else .. fi;

Problem: Define your own version of the absolute value function.

A solution:

> myabs := proc(x) if x > 0 then x else -x fi end;

> myabs(-23);

> plot(myabs,-2..2,scaling=constrained,title=`my absolute value`); # to see what it looks like.

A Brief Vocabulary of Maple Words

Here are some Maple words useful in mathematical problem solving, together with examples of their usage. For more information on these words and others, look at the helpsheets and use the help browser.

> y := (x+3)/tan(x^2-1); # use 'colon-equal' to make assignments.

> collect(x*2 + 4*x,x); # collects like powers of x.

> diff(cos(x),x); # calculates the derivative

> D(cos); # the differential operator

> y := denom((a+b)/(e+f)); # assigns e+f to y.

> y := 'y'; # makes y a variable again.

> evalc((2+3*I)^3); # performs complex arithmetic

> evalf(1/2^9); #evaluates 1/2^9 to a decimal number

> expand((x+b)^7); # expands the product

> p := x^2+5*x+6; # assigns the quadratic to p.

> factor(p); # factors the polynomial

> fsolve(x^5-3*x=1,x,0..2); # solve eqn for x in 0..2

> int(x*exp(x),x); # returns an antiderivative.

> Int(x*exp(x),x=0..1); # A passive integral.

> map(x->x^2,[1,3,2,5]); # returns a list of squares.

> nops([3,4,x,1]); # returns the number of terms in the list.

> numer((a+b)/c); # gives numerator, here a+b

> op([3,4,1,x]); # strips the brackets off the list

> plot(x^2+x, x=-3..3); # plots x^2+x as x goes from -3 to 3.

> plot3d(x^2+y,x=-2..2,y=0..2); # plots a surface

> f := x -> x^2; # defines the squaring function.

> f(3); # then returns 9.

> quo((x^4-4),(x^2-2),x); # divides polynomials

> iquo(23,2) ; # divides the integers

> rem((x^4-4*x+3),(x^2-2),x); # gives the remainder

> irem(23,2) ; # gives the integer remainder

> restart; # very handy. This word resets all assignments.

> eq1 := x^2 + 3*x -1 = a; # assigns the equation

> rhs(eq1); # yields the righthand side of eq1. There is also an lhs.

> simplify(a/x+b/y); # sometimes simplifies expr.

> solve(a*x+4*y=0,x); # solve the equation for x.

> subs(x=5,x^2+x); # substitute 5 for x where it occurs in x^2+x.

> i := 'i'; # makes i a variable again

> sum((i^2,i=2..9)); # add up the 2nd thru 9th squares

>

Maple's mathematical vocabulary is extensive, but it can never be complete. That's because we are always discovering new ways to do things. The methods can then be defined in a Maple procedure.

One way to develop the definition is in a series of input cells: For example, suppose we wanted to define a word to solve a quadratic equation a . We want the inputs to be the coefficients a,b,c of the equation, and the output to be the roots and a message describing the natrue of the roots. So given the inputs values in an input cell. Now develop the body of the procedure in an input cell below it. Thus the nature of the roots is determined by the discriminant , so we need to use a conditional statement here.

> a := 3 : b:= 0: c := 5:

> if b^2 - 4*a*c < 0 then print("negative discriminant. no real roots.")
elif b^2 - 4*a*c = 0 then print("discriminant is 0. 1 real root.");
(-b +sqrt(b^2-4*a*c))/(2*a)
else print("discriminant is positive, two real roots.");
(-b +sqrt(b^2-4*a*c))/(2*a),(-b -sqrt(b^2-4*a*c))/(2*a) fi;

After changing the values of a, b, and c in the input cell and testing the body of the procudure, we can define the procedure in an input cell. Use the copy and paste item in the edit menu to put the body into the cell below then at the top put the 'proc line' and at the bottom put the 'end line'.

> quadroots := proc(a,b,c) # the proc line
if b^2 - 4*a*c < 0 then print("negative discriminant. no real roots.")
elif b^2 - 4*a*c = 0 then print("discriminant is 0. 1 real root.");
(-b +sqrt(b^2-4*a*c))/(2*a)
else print("discriminant is positive, two real roots.");
(-b +sqrt(b^2-4*a*c))/(2*a),(-b -sqrt(b^2-4*a*c))/(2*a) fi;
end; # the end line

Now, test the procedure again

At this point, you have added a word to the Maple language. It can be used just like any of the other words. It is not a permanent addition, however. The next time you run Maple, it won't be there, unless you make some special effort.

One way to keep all your procedures together is to put them into a "package". A package in Maple is a table whose indices are names of procedures and whose entries are the bodies of those procedures. For example, in this worksheet, we have defined two procedures that we might like to keep in a package, quadroots and one further back myabs.

We could call the package 'mystuff'.

> mystuff := table([]);

> mystuff[quadroots]:= proc(a,b,c) # the proc line
if b^2 - 4*a*c < 0 then print("negative discriminant. no real roots.")
elif b^2 - 4*a*c = 0 then print("discriminant is 0. 1 real root.");
(-b +sqrt(b^2-4*a*c))/(2*a)
else print("discriminant is positive, two real roots.");
(-b +sqrt(b^2-4*a*c))/(2*a),(-b -sqrt(b^2-4*a*c))/(2*a) fi;
end: # the end line
mystuff[myabs]:= proc(x) if x > 0 then x else -x fi end:
with(mystuff);

Now in order to use the procedures in the 'mystuff' package, load a worksheet containing the package and execute the cell containing the definitions. Include the line with(mystuff) at the bottom to complete the loading process.

Using the Packages that come with Maple

There are many packages that come with Maple, for example, plots and plottools are packages of words used to draw pictures, student is a package of words for calculus students, numtheory is a package of number theory words, linalg a package of linear algebra words, geometry a package of words for analytic geometry, and so on. To see the words in a package and at the same time make them usable, load the package using with

> with(plots);

Just like the regular vocabulary, these words all have help pages too. A good strategy when you have a task of some sort to do is to scan for words which might help you complete the task.

Example: Draw a blue ball and a red cone.

A solution. There might be some words in the plottools package to help here.

> with(plottools);

Yep. cone and sphere are the words we are looking for. What is their syntax? we can type

> example(cone);

This brings up the helpsheet for cone and goes to the examples section. copy the example and paste it into your worksheet.

> icecream := cone([0,0,-1],0.7,color=gold), sphere([0,0,0.1],0.6,color=brown):
plots[display](icecream, scaling=constrained, style=patch);

This does not solve our problem, but we can modify it to solve the problem. All we have to do is change colors.

> icecream := cone([0,0,-1],0.7,color=red), sphere([0,0,.1],0.6,color=blue):
plots[display](icecream, scaling=constrained);

Note the use of the word plots[display]. This is used to display several plots in the same picture. By using it as plots[display] instead of in the form display, it is not necessary to have loaded the plots package into vocabulary in order to use it. (If you say display(icecream) and have not loaded the plots package by saying with(plots) first, the output will be the input 'display(icecream)'.)

>

The linalg package

The linalg package of word is one of the most useful in Maple. To load the package, use with(linalg);

> with(linalg);

Warning, new definition for norm

Warning, new definition for trace

Most of the algorithms in Ma 322 (as well as many that aren't) can be found in this list. For example, the dot product of two vectors can be computed using the word linalg[dotprod]. If you have loaded in the linalg package in a worksheet, you can use the short name dotprod .

> dotprod([2,1,3],[4,2,1]);

A vector can be defined in maple as a list or as a vector

> A := [3,2,3];

> B := vector([3,2,1]);

> dotprod(A,B);

To get the angle between two vectors, use linalg[angle]. For example, if I want to know the angle between A and A + 2*B

> ang:= angle(A,A+2*B) ;

To convert the angle to a decimal number use evalf

> evalf(ang);

To convert the angle to degrees, we can multiple by 180/Pi

> evalf(180/Pi*angle(A,A+2*B));

A matrix is entered row by row. So, for example to define the 2 by 3 matrix whose top row is [3,1,5] and whose bottom row is [6,5,4]

> C := matrix(2,3,[3,1,5,6,5,4]);

To get the norm of a vector, take the square root of the dotproduct of the vector with itself.

> sqrt(dotprod(A,A));

Randmatrix is used to generate a matrix with some random entries.

> E:= randmatrix(2,3);

To add two matrices of the same size use matadd or &+ (together with evalm )

> evalm(C &+ E);

Row operations on matrices are important in linear algebra. One particular one is to add a scalar multiple of one row of a matrix to another row of that matrix. So, to add 5 times the first row of E above to the second row, use addrow

>

Matrix multiplication is especially important operation also. Use multiply or &* (together with evalm ) to do that

> F := matrix(3,2,[1,2,4,5,0,-3]);

> multiply(E,F);

> evalm(E &* F);

The best way to learn to use the words in linalg is to work problems in linear algebra. Over the course of a semester, you can become fairly proficient at using linalg to do (or check) the computation you need to do.

Making Movies

A movie (or animation) is a sequence of frames displayed one after the other. A well conceived animation can be of great use in gaining an understanding of some phenomena. They are also fun to make. Here is an example:

Example: Have a blue ball move up out of a red cone.

> icecream := cone([0,0,-1],0.7,color=red), sphere([0,0,.1],0.6,color=blue):
plots[display](icecream, scaling=constrained);

This is the first frame of our movie. What has to change in order for the ball to rise up out of the cone? the z-coordinate of the center of the ball. If we define our frame like so

> frame := t ->
plots[display](cone([0,0,-1],0.7,color=red), sphere([0,0,t],0.6,color=blue), scaling=constrained);

> frame(2);

>

Now in order to see the ball clearly we have to change the orientation and put in some axes.

> frame := t ->
plots[display](cone([0,0,-1],0.7,color=red), sphere([0,0,t],0.6,color=blue), scaling=constrained,axes=boxed,orientation=[50,70]);

> frame(2);

Now we can make a movie using plots[display] with the option insequence=true

> plots[display](seq(frame(i/2),i=1..5),insequence=true,scaling=constrained);

>

To run the animation, activate the plot and press the play button.

Trouble Shooting Notes

Learning to use Maple can be an extremely frustrating experience, if you let it. There are some types of errors which occur from the beginning that can be spotted and corrected easily by a person fluent in Maple, so if you have access to such a person, use him or her.

Here are a few suggestions that may be of use when you're stuck with a worksheet that's not working like it should.

Important! Loading an old Maple worksheet does not excute it. This is something you must do separately, either one cell at a time or all at once.

Also important! Remember that you can rexecute any cell in the worksheet at any time. This can lead to confusion about what you did last, because it may not be what is just above.

Use help: There is a help sheet with examples for every Maple word. A quick read thru will often clear up syntax problems. One very common early mistake is to leave out the parentheses around the inputs of a word. For example, typing

> plot x^2;

Syntax error, missing operator or `;`

will get you a syntax error, because you left out the parentheses.

>

The maple prompt is `>` . You can begin entering input after it. Make sure you are typing into an input cell, if you are expecting output.

End maple statements with a semicolon `;` or colon `:` . Maple suppresses output when the command line ends with a colon. Maple does not process until it comes to a (semi)colon. If you are getting no output when you should be, try feeding in a semicolon. This often works.

> p := expand((a+b)^5);

> p;

> q := expand((1+x)^9):

> q;

>

When in doubt, put in parentheses. For example, (x+3)/(x-3) is very different from x+3 / x-3 .

> (x+3)/(x-3),x+3 / x-3 ;

>

Make sure your variables are variable . You may have assigned a value, say 3, to x in a previous problem. To make x a variable again, type x := 'x': . Use the forward quote ' key, just below the double quote " here. If you forget this, strange things might happen. One way to handle this is to keep an input cell of variables used.

> x := 3;

> x := 'x';

>

Use restart; By typing restart; in an input cell and pressing enter, you clear all assignments, and start with a clean slate. This fixes a lot of problems fast, but you will need to re-execute input cells.

> hello := yes;

> hello;

> restart;

> hello;

> `this is a long name` := 12;

> `this is a long name`;

> check := "do not worry";

> check;

Do not forget to end loops with od , `if` statements with fi , and procedures with end . If you start a loop with do , Maple does not begin processing until it finds the end of the loop, which is signaled by the word od ; The same applies to the if .. then ... fi; and proc ... end; contructions. If you are getting no output when you should be, try feeding an od; , fi; , or end; This often works.

>

>

Unwanted output?: Is there output you need but don't want to see? Use a colon `:` instead of a semicolon to end the Maple statement which generates the output.

> unapply(x^2-100,x);

> printlevel:= 10;

>

> unapply(x^2-200,x);

{--> enter unapply, args = x^2-200, x

<-- exit unapply (now at top level) = proc (x) options operator, arrow; x^2-200 end}

> printlevel:=1;

Are all words you are using defined? Have you executed the input cells containing the procedures you need? Have you loaded the packages containing the words you need? Undefined words are simply returned by Maple. Hint: When using words from packages in procedure definitions, use the full name, e.g, use plots[display] instead of display.

> thisword := proc(x) x^2 + 10 end;

> thisword(3);

> restart;

> thisword(3);

>

> debug(thisword);

> thisword(3);

{--> enter thisword, args = 3

<-- exit thisword (now at top level) = 19}

> undebug(thisword);

> thisword(3);

>

> interface(verboseproc=2);

> print(plot):

>