Hi!
I have the following question related to the ccode function of the symbolic toolbox.
Let us consider the following piece of code:
syms a b real
ccode(atan2(a,b))
the result is:
' t0 = log((a*sqrt(-1.0)+b)/fabs(a*sqrt(-1.0)+b))*-sqrt(-1.0);'
Questions for the MathWorks:
1. Why ccode replace the atan2 function (which is available in c) with such log implementation?
2. There is a way to prevent such replacement (some additional optional parameter?)
The following Matlab script has been written to generate I/O pairs for the atan2 function to compare the output of the Matlab atan2 vs the C vs the ccode output:
p = -2:1:2;
[X,Y] = meshgrid(p,p);
Z = zeros(size(X));
for i=1:size(X,1)
for j=1:size(X,2)
Z(i,j) = atan2(Y(i,j),X(i,j));
end
end
And with those data I ran the following C code (Visual Studio)
#include "stdafx.h"
#include "math.h"
#include "complex.h"
double Atan2(double a, double b) {
return log((a*sqrt(-1.0) + b) / fabs(a*sqrt(-1.0) + b))*-sqrt(-1.0);
}
int main()
{
const unsigned int nTest = 25;
const double adX[nTest] = { -2.000000, -2.000000, -2.000000, -2.000000, -2.000000, -1.000000, -1.000000, -1.000000, -1.000000, -1.000000, 0.000000, 0.000000, 0.000000, 0.000000, 0.000000, 1.000000, 1.000000, 1.000000, 1.000000, 1.000000, 2.000000, 2.000000, 2.000000, 2.000000, 2.000000, };
const double adY[nTest] = { -2.000000, -1.000000, 0.000000, 1.000000, 2.000000, -2.000000, -1.000000, 0.000000, 1.000000, 2.000000, -2.000000, -1.000000, 0.000000, 1.000000, 2.000000, -2.000000, -1.000000, 0.000000, 1.000000, 2.000000, -2.000000, -1.000000, 0.000000, 1.000000, 2.000000, };
const double adZ[nTest] = { -2.356194, -2.677945, 3.141593, 2.677945, 2.356194, -2.034444, -2.356194, 3.141593, 2.356194, 2.034444, -1.570796, -1.570796, 0.000000, 1.570796, 1.570796, -1.107149, -0.785398, 0.000000, 0.785398, 1.107149, -0.785398, -0.463648, 0.000000, 0.463648, 0.785398, };
unsigned int nIdx = 0;
for (nIdx = 0; nIdx < nTest; nIdx++) {
printf("atan2(%+05.5f,%+05.5f)= Matlab(%+05.5f) C(%+05.5f) CCODE(%+05.5f)\n",
adY[nIdx], adX[nIdx],
adZ[nIdx],
atan2(adY[nIdx], adX[nIdx]),
Atan2(adY[nIdx], adX[nIdx]));
}
scanf("%d", &nIdx);
return 0;
}
The results are presented here:
atan2(-2.00000,-2.00000)= Matlab(-2.35619) C(-2.35619) CCODE(-nan(ind))
atan2(-1.00000,-2.00000)= Matlab(-2.67794) C(-2.67795) CCODE(-nan(ind))
atan2(+0.00000,-2.00000)= Matlab(+3.14159) C(+3.14159) CCODE(-nan(ind))
atan2(+1.00000,-2.00000)= Matlab(+2.67794) C(+2.67795) CCODE(-nan(ind))
atan2(+2.00000,-2.00000)= Matlab(+2.35619) C(+2.35619) CCODE(-nan(ind))
atan2(-2.00000,-1.00000)= Matlab(-2.03444) C(-2.03444) CCODE(-nan(ind))
atan2(-1.00000,-1.00000)= Matlab(-2.35619) C(-2.35619) CCODE(-nan(ind))
atan2(+0.00000,-1.00000)= Matlab(+3.14159) C(+3.14159) CCODE(-nan(ind))
atan2(+1.00000,-1.00000)= Matlab(+2.35619) C(+2.35619) CCODE(-nan(ind))
atan2(+2.00000,-1.00000)= Matlab(+2.03444) C(+2.03444) CCODE(-nan(ind))
atan2(-2.00000,+0.00000)= Matlab(-1.57080) C(-1.57080) CCODE(-nan(ind))
atan2(-1.00000,+0.00000)= Matlab(-1.57080) C(-1.57080) CCODE(-nan(ind))
atan2(+0.00000,+0.00000)= Matlab(+0.00000) C(+0.00000) CCODE(-nan(ind))
atan2(+1.00000,+0.00000)= Matlab(+1.57080) C(+1.57080) CCODE(-nan(ind))
atan2(+2.00000,+0.00000)= Matlab(+1.57080) C(+1.57080) CCODE(-nan(ind))
atan2(-2.00000,+1.00000)= Matlab(-1.10715) C(-1.10715) CCODE(-nan(ind))
atan2(-1.00000,+1.00000)= Matlab(-0.78540) C(-0.78540) CCODE(-nan(ind))
atan2(+0.00000,+1.00000)= Matlab(+0.00000) C(+0.00000) CCODE(-nan(ind))
atan2(+1.00000,+1.00000)= Matlab(+0.78540) C(+0.78540) CCODE(-nan(ind))
atan2(+2.00000,+1.00000)= Matlab(+1.10715) C(+1.10715) CCODE(-nan(ind))
atan2(-2.00000,+2.00000)= Matlab(-0.78540) C(-0.78540) CCODE(-nan(ind))
atan2(-1.00000,+2.00000)= Matlab(-0.46365) C(-0.46365) CCODE(-nan(ind))
atan2(+0.00000,+2.00000)= Matlab(+0.00000) C(+0.00000) CCODE(-nan(ind))
atan2(+1.00000,+2.00000)= Matlab(+0.46365) C(+0.46365) CCODE(-nan(ind))
atan2(+2.00000,+2.00000)= Matlab(+0.78540) C(+0.78540) CCODE(-nan(ind))
How can I fix this? Hoping to receive a valid answer asap.
Vincenzo
