reason for a code written in C and matlab giving different output

[tangled09]

The codes (C and matlab) are exactly same (operations wise) and same value of epsilon is used in both the codes. Still they give different output, what could be the reason for it.

[VictorN]

1. What is "epsilon"?
2. What is the type of the "output"?
3. What was the "difference" between the "outputs"?

[tangled09]

1.This epsilon is used in if statements for making comparisons. epsilon in matlab is 2.2204e-16 .

I use " #define eps 2.2204e-16 " in C

2. The output is obtained by using arithmetic operations and comparisons on the initial data (which is taken to be exactly same for both C and Matlab code)

3. The contour plots of C and Matlab outputs differ slightly

[TubularX]

3. The contour plots of C and Matlab outputs differ slightly

How slightly? Some numbers can't be represented exactly, so they will be rounded off. The deviation can then increase for every arithmetic operation.

[2kaud]

What precision are you using for real numbers in c and in Matlab? In c/c++ there are several different precision types that can be used - eg float, double, long double.

For MS VS, see
https://msdn.microsoft.com/en-us/library/cc953fe1.aspx
https://msdn.microsoft.com/en-us/library/s3f49ktz.aspx

Also note that in c the ordering of expression evaluation can have an effect on the accuracy of the result.