How is it possible that I get different answers for the same equations in two codes?

I am writing a code for the thermomechanical behaviour of an one-dimensional element.

From line 146-150 in the first code (Transient_ThermomechanicalCoupling) i expect an answer for TRAC which is not zero. However the answer is zero. In the other code (VERGELIJKINGTRAC) i have the same variables and get an answer that is not zero. I can't find the problem and have been looking for it for days now... It might be a small error but i can't find it. I hope someone could help me.

Answer 1

[Image Analyst]

They're totally different programs.

Anyway, perhaps you haven't read the FAQ: http://matlab.wikia.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F - maybe it's a precision issue.

[Rick Titulaer]

Yes the programs are different, but they use the same matrices K and UT. However the answer is not the same.

[Image Analyst]

Did you directly copy, not by hand but by control-c and control-v, the assignments from the original to the copy? What steps are you using to switch the variables? Is each set of variables in an m-file and then you call that? It doesn't look like it. Tell me how I can reproduce the problem with both sets of parameters.

[Rick Titulaer]

In the first m-file (Transient_ThermomechanicalCoupling) the K matrix is calculated in line 72-98. Then the UT is calculated with line 146. Then i directly copied with control-c and control-v the matrix K and vector UT into the other m-file (VERGELIJKINGTRAC). THen when i calculate the TRAC in VERGELIJKINGTRAC i get values for all the five nodes. When i calculate the TRAC in Transient_ThermomechanicaCoupling i only get one value for the second node and 4 nodes zero.

I think it is strange because i use the same matrix and vector?

[Rick Titulaer]

The UT vector i calculate with the first m-file (Transient_ThermomechanicalCoupling) is

7.71262898705694e-06 1.53556097935277e-05 6.34013739884418e-06 -5.21137363050607e-06 -7.71260858096823e-06 293.031375121031 293.026829323982 292.861307169013 293.527944249668

And the K matrix is:

1.50769066666667 -0.753845333333333 0 0 0 -1.15500000000000e-05 1.15500000000000e-05 0 0 -0.753845333333333 0.753845333333333 -0.753845333333333 0.0942306666666667 0 -2.88750000000000e-06 0 2.88750000000000e-06 0 0 -0.753845333333333 1.50769066666667 -0.753845333333333 0 0 -1.15500000000000e-05 1.15500000000000e-05 0 0 0.0942306666666667 -0.753845333333333 0.753845333333333 -0.753845333333333 0 -2.88750000000000e-06 0 2.88750000000000e-06 0 0 0 -0.753845333333333 1.50769066666667 0 0 -1.15500000000000e-05 1.15500000000000e-05 0 0 0 0 0 0.00675266666666667 -8.60000000000000e-05 0 0 0 0 0 0 0 -8.60000000000000e-05 0.000172000000000000 -8.60000000000000e-05 0 0 0 0 0 0 0 -8.60000000000000e-05 0.000172000000000000 -8.60000000000000e-05 0 0 0 0 0 0 0 -8.60000000000000e-05 0.0167526666666667

These values i copied to the other m-file and calculate it. But the answers are different.