Re: [Mingw-msys] pow(5,2)=24 ?????!!!!!

["Michael Chen" <vancouver.michael@xxxxxxxxx>]

  int s = (int) pow(l,d);
  printf("%d\t%d\t%d\n",l,d,s);


And I tried several (l,d), results are:
2 2 4
3 2 9
4 2 16
5 2 24  <= this one is wrong
6 2 36
....

What shall I use then? my variable s, l, and d are integers!

Michael Chen


jpnolan@xxxxxxxxxxxx

On 9/7/07, John Nolan <jpnolan@xxxxxxxxxxxx> wrote:

Oops, I meant 24.9999... being rounded to 24. John

John Nolan < jpnolan@xxxxxxxxxxxx>

John Nolan <jpnolan@xxxxxxxxxxxx>
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09/07/2007 04:16 PM

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Subject	Re: [Mingw-msys] pow(5,2)=24 ?????!!!!!

The definition of pow( ) takes doubles for both arguments. Try it with double arguments and double result. Might also have rounding issues with the answer, e.g. 14.9999999... being truncated to 24. John

...........................................................................

John P. Nolan
Math/Stat Department
227 Gray Hall
American University
4400 Massachusetts Avenue, NW
Washington, DC 20016-8050

jpnolan@xxxxxxxxxxxx
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http://academic2.american.edu/~jpnolan
...........................................................................

"Michael Chen" < vancouver.michael@xxxxxxxxx>

"Michael Chen" <vancouver.michael@xxxxxxxxx>
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09/07/2007 03:56 PM

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Subject	[Mingw-msys] pow(5,2)=24 ?????!!!!!

Hi, there,

I spent several hours and still get pow(5,2)=24 at the last line of
the code, please help!

Environment:
Windows XP
gcc.exe (GCC) 3.4.2 (mingw-special)

compile command:
gcc -g -Wall -lm spclen.c

Thanks for your help!

Michael Chen

------------------------------------------------------
#include <math.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

int main()
{

double s=0;
int Tl=0,Ti=0;

s=0;Tl=0;Ti=0;
s=combinationformula(5,2,intexy11,&Tl,&Ti);
printf("%f\t%d\t%d\n",s,Tl,Ti);


}


double combinationformula(int l, int  d, double (*f)(int, double *),
int *Tl,int *Ti)
{
int i,j;
int k1norm;
int sign;
int *I;
int *idx;
double s=0;
double cho=0.0;

*Ti=0;
idx = idxtree(l,d,Tl);

....

}

int *idxtree(int L, int D, int *T)
{
int i,j;
int s;//length
int tr;//total of a row

int *p;//point to the full tree
int *r;//point to the reduced tree
int *f;//point to the flags

*T=0;//total of multi index

s = (int)pow(L,D); // wrong here, when L=5 D=2, I got 24!!!


...
}

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