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Re: equivalent to C pointer

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  Re: equivalent to C pointer David Robinow <drobinow@gmail.com> - 2013-04-18 14:04 -0400

#43846 — Re: equivalent to C pointer

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On Thu, Apr 18, 2013 at 1:06 PM, abdelkader belahcene
<abelahcene@gmail.com>wrote:

> Hi everybody,
>
> I am new to python  and I am discovering it.
> I know C well,
> and want to know if python knows how to manage Pointers
> like pointer to function  here is a C example how to write it in python
> Intergration with trapeze method
>
> When we write Trapeze   ( at the compilation level) we don't know which
> functions
> Fonc  to handle.      Here for example we use  sin and a user defined  F1
> The program is attached too
>
> #include <stdio.h>
> #include <math.h>
>
> double F1 (double x){
>         return x*x;
> }
> double Trapeze(double Fonc(double ),
>                                 double left, double right, double step){
>   double X1, X0, Y0, Y1, Z = 0;
>   for(X0=left; X0 < right ; X0 = X0 + step) {
>     X1 = X0 + step;
>     Y1 = Fonc(X1);    Y0 = Fonc(X0);
>     Z  += (Y1 + Y0) * step * 0.5;
>   }
>    return Z;
> }
> int  main(){
>   double y;
>   y=Trapeze(sin, -2.5, 3.2, 0.1);
>   printf("\n\tValue for sin  is : \t %8.3lf ", y);
>   y=Trapeze(F1, 0, 3, 0.1);
>   printf("\n\tValue for F1 is : \t %8.3lf ", y);
>   return 0;
> }
> /**
>     Value for sin  is :         0.197
>     Value for F1 is :          9.005
>     */
>
> Python doesn't have pointers, but don't let that bother you.
A python version is actually a lot simpler.
See below (I didn't bother with getting the print formats just right)
--
import math
def F1(x):
    return x*x

def Trapeze(f, left, right, step):
    X0 = left
    Z = 0.0
    while (X0 < right):
        X1 = X0 + step
        Y1 = f(X1)
        Y0 = f(X0)
        Z += (Y1 + Y0) * step * 0.5
        X0 = X1
    return Z

def main():
    y = Trapeze(math.sin, -2.5, 3.2, 0.1)
    print("Value for sin is:{0} ".format(y))
    y = Trapeze(F1, 0, 3, 0.1)
    print("Value for F1 is {0} ".format(y))

if __name__ == "__main__":
    main()

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