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Date: Thu, 18 Apr 2013 14:04:49 -0400
Subject: Re: equivalent to C pointer
From: David Robinow <drobinow@gmail.com>
To: abdelkader belahcene <abelahcene@gmail.com>
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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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Content-Transfer-Encoding: quoted-printable

<div class=3D"gmail_quote">On Thu, Apr 18, 2013 at 1:06 PM, abdelkader bela=
hcene <span dir=3D"ltr">&lt;<a href=3D"mailto:abelahcene@gmail.com" target=
=3D"_blank">abelahcene@gmail.com</a>&gt;</span> wrote:<br><blockquote class=
=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padd=
ing-left:1ex">
<div dir=3D"ltr"><div><div><div><div><div><div><div>Hi everybody,=C2=A0 <br=
><br></div>I am new to python=C2=A0 and I am discovering it.<br></div>I kno=
w C well,<br></div>and want to know if python knows how to manage Pointers<=
br></div>

like pointer to function=C2=A0 here is a C example how to write it in pytho=
n<br></div><div>Intergration with trapeze method<br></div><div><br></div>Wh=
en we write Trapeze =C2=A0 ( at the compilation level) we don&#39;t know wh=
ich functions <br>

</div>Fonc=C2=A0 to handle.=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 Here for example =
we use=C2=A0 sin and a user defined=C2=A0 F1<br></div>The program is attach=
ed too<br><div><br><div><div><div><div><div><div><div><div><div>#include &l=
t;stdio.h&gt;<br>#include &lt;math.h&gt;<br>

=C2=A0<br>double F1 (double x){ <br>=C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 r=
eturn x*x; <br>}<br>double Trapeze(double Fonc(double ), <br>=C2=A0=C2=A0=
=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0=C2=
=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 double l=
eft, double right, double step){<br>=C2=A0 double X1, X0, Y0, Y1, Z =3D 0;=
=C2=A0=C2=A0=C2=A0 <br>=C2=A0 for(X0=3Dleft; X0 &lt; right ; X0 =3D X0 + st=
ep) {<br>

=C2=A0=C2=A0=C2=A0 X1 =3D X0 + step;<br>=C2=A0=C2=A0=C2=A0 Y1 =3D Fonc(X1);=
=C2=A0=C2=A0=C2=A0 Y0 =3D Fonc(X0);<br>=C2=A0=C2=A0=C2=A0 Z=C2=A0 +=3D (Y1 =
+ Y0) * step * 0.5;<br>=C2=A0 }<br>=C2=A0=C2=A0 return Z;<br>}<br>int=C2=A0=
 main(){ <br>=C2=A0 double y;<br>=C2=A0 y=3DTrapeze(sin, -2.5, 3.2, 0.1);<b=
r>=C2=A0 printf(&quot;\n\tValue for sin=C2=A0 is : \t %8.3lf &quot;, y);<br=
>

=C2=A0 y=3DTrapeze(F1, 0, 3, 0.1);<br>=C2=A0 printf(&quot;\n\tValue for F1 =
is : \t %8.3lf &quot;, y);<br>=C2=A0 return 0;<br>} <br>/**<br>=C2=A0=C2=A0=
=C2=A0 Value for sin=C2=A0 is : =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0 0.197=
 <br>=C2=A0=C2=A0=C2=A0 Value for F1 is : =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=
=C2=A0=C2=A0 9.005<br>=C2=A0=C2=A0=C2=A0 */<br></div><br>
</div></div></div></div></div></div></div></div></div></div></blockquote></=
div>Python doesn&#39;t have pointers, but don&#39;t let that bother you.<br=
>A python version is actually a lot simpler.<br>See below (I didn&#39;t bot=
her with getting the print formats just right)<br>
--<br>import math<br>def F1(x):<br>=C2=A0=C2=A0=C2=A0 return x*x<br><br>def=
 Trapeze(f, left, right, step):<br>=C2=A0=C2=A0=C2=A0 X0 =3D left<br>=C2=A0=
=C2=A0=C2=A0 Z =3D 0.0<br>=C2=A0=C2=A0=C2=A0 while (X0 &lt; right):<br>=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 X1 =3D X0 + step<br>=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0 Y1 =3D f(X1)<br>=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0 Y0 =3D f(X0)<br>
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 Z +=3D (Y1 + Y0) * step * 0.5<br=
>=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 X0 =3D X1<br>=C2=A0=C2=A0=C2=A0=
 return Z<br><br>def main():<br>=C2=A0=C2=A0=C2=A0 y =3D Trapeze(math.sin, =
-2.5, 3.2, 0.1)<br>=C2=A0=C2=A0=C2=A0 print(&quot;Value for sin is:{0} &quo=
t;.format(y))<br>=C2=A0=C2=A0=C2=A0 y =3D Trapeze(F1, 0, 3, 0.1)<br>
=C2=A0=C2=A0=C2=A0 print(&quot;Value for F1 is {0} &quot;.format(y))<br><br=
>if __name__ =3D=3D &quot;__main__&quot;:<br>=C2=A0=C2=A0=C2=A0 main()<br><=
br>

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