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Functions in Maple 教授：蔡桂宏 博士 學生：柯建豪 學號： 95356026 95503 統資軟體課程講義

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1.1 Introduction Understanding functions in Maple is also a good starting point for our discussions about Maple programming. There are two distinct ways to represent mathematical functions in Maple. That is Maple expression ( := ) and a Maple function ( -> ).

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1.2 Functions in Mathematics the formula has as its domain the set of all real numbers, its codomain is the set of all positive real numbers. the formula has as its domain the set of all positive real numbers, its codomain is the set of all positive real numbers. the formula has as its domain the set of all negative real numbers, its codomain is the set of all positive real numbers.

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the function f is not invertible. The inverse of the function g is. The inverse of the function h is. So f, g, and h all have the same formula (i.e., rule) but they are not the same function. The domain and codomain are important parts of the definition of a mathematical function.

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1.3 Functions in Maple These two ways of representing mathematical functions are not equivalent. And it is subtle and non-obvious. A Maple function is something defined using arrow notation ( ->). A Maple expression is something defined using ( := ). x -> x^2; x -> a*x^2; (x,a) -> a*x^2;

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. Maple will treat all unassigned names (i.e., all unknowns) as variables. The mathematical function. g := x -> x^2 – 1; g(2); g(x) := x^2-1; g(2);

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g := cos + ln; k := x -> cos(x) + ln(x); g(Pi); k(Pi); h := cos + (x -> 3*x-1); h(z);

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f := x -> (1 + x^2)/x^3; g := (1 + (x -> x^2))/(x -> x^3); h := (1 + (z -> z^2))/(y -> y^3); f(1); g(1); h(1); m := x -> (1 + exp(x))/x^3; n := (1 + exp)/(x -> x^3); m(1); n(1);

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f := x^2; g := x -> 2 * x^3 * f; g(x); g(2); f := x -> x^2; g := 2 * (x -> x^3) * f; g(x); g(2);

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1.4 Expressions vs. functions: Some puzzles The following examples are meant to show that there are still a lot of subtle things to learn about variables and functions and how Maple handles them.

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Puzzle 1 f1 := x^2+1; f2 := y^2+1; f3 := f1 + f2; f3 is a function of two variables. g1 := x -> x^2+1; g2 := y -> y^2+1; g3 := g1 + g2; g3(x); g3 is not a function of two variables.

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Puzzle 2 x:='x': a:=1: b:=2: c:=3: a*x^2+b*x+c; f := unapply( a*x^2+b*x+c, x ); g := x -> a*x^2+b*x+c; f(x); g(x); D(f); D(g); p := x^2 + sin(x) + 1; p(2); p := unapply(p,x); p(2);

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Puzzle 3 plot( x^2, x=-10..10 ); plot( x->x^2, -10..10 ); plot( x^2, -10..10 ); plot( x->x^2, x=-10..10 );

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x := 5; plot( x^2, x=-10..10 ); plot( x->x^2, -10..10 );

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Puzzle 4 f := x^2; f := x*f; f; g := x -> x^2; g := x -> x*g(x); g(x);

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Puzzle 5 x^2; f := %; plot( f, x=-3..3 ); x^2; g := x -> %; plot( g, -3..3 );

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1.5 Working with expressions and Maple functions (review) g := x -> x^2-3*x-10; g(x); g; print(g); eval(g); op(g);

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plot( a*x^2, -5..5 ); plot( x->a*x^2, -5..5 ); plot3d( (x,a)->a*x^2, -5..5, -10..10 );

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We wanted to evaluate our mathematical function at a point, say at 1. f := x^2 - 3*x-10; g := x -> x^2-3*x-10; subs( x=1, f ); eval( f, x=1 ); g(1); f(1); subs( x=1, g );

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eval( f, x=1 ); subs( x=1, f ); Think of reading eval( f, x=1) as " evaluate f at x=1" and think of reading subs (x=1,f) as " substitute x=1 into f". factor( f ); factor( g(x) ); factor( f (x) ); factor( g );

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diff( f, x ); D( g ); diff command needed a reference to x in it but the D command did not. D( f ); diff( g, x );

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Let us do an example of combining two mathematical functions f and g by composing them to make a new function. For the expression: f := x^2 + 3*x; g := x + 1; h := subs( x=g, f ); subs(x=1, h);

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For the function: f := x -> x^2 + 3*x; g := x -> x + 1; h := f@g; h(x); h(1);

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Let us do an example of representing a mathematical function of two variables. Here is an expression in two variables. f := (x^2+y^2)/(x+x*y); g := (x,y) -> (x^2+y^2)/(x+x*y); subs( x=1, y=2, f ); eval( f, {x=1, y=2} ); g(1,2); simplify( f ); simplify( g(x,y) );

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Here is how we compute partial derivatives of the expression. diff( f, x ); simplify( % ); diff( f, y ); simplify( % ); D[1](g); simplify( %(x,y) ); D[2](g); simplify( %(x,y) );

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1.6 Anonymous functions and expressions (review) Here we define an anonymous function and then evaluate, differentiate, and integrate it. (z -> z^2*tan(z))(Pi/4); x -> x^3 + 2*x; %(2); D( % ); int( (%%)(x), x );

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These next two commands show again that defining a function and naming a function are two distinct steps. z -> z/sqrt(1-z); f := %;

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f := ((x,y) -> x^2) + ((x,y) -> y^3); f(u,v); f(2,3); g := (x -> x^2) + (y -> y^3); g(u,v); g(2,3);

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plot(w^3+1, w=-1..1); plot( ((x,y)->x^3-y^3)(w,-1), w = -1..1 ); plot( w->(((x,y)->x^3-y^3)(w,-1)), -1..1 );

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1.7. Functions that return a function (optional) f := a -> ( y->a*y ); f(3); f(3)(4);

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f := (x,y) -> 3*x^2+5*y^2; f(x,3); fx3 := x -> f(x,3); fx3(x); slice_f_with_y_fixed := c -> ( x->f(x,c) ); fx3 := slice_f_with_y_fixed(3); fx3(x);

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The End ! Thank you for your listening !

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