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From: Etienne on 29 Jul 2010 20:15
Hi Folks

I am trying to calculate the derivatiaves of a function. However, when I implement the equations in a matlab function, and then in a simulink function, the simulink model runs a lot slower. I ran the profiler and get the results at the end of the message. Line 11 does the same as 18 and 19. Why the massive difference? I have disabled the simulink autosave function, checked for writing to the workspace etc, but I am not sure if there might be other simulink settings I can try.

Thanks

Etienne

===============================================
time calls line
1 function [f,o,dfdu,dfdp]=absimfunc(par,u,ijac)
2 %
3 % function file for demo ab
4 %
1.11 1203138 5 f=[0,0];
0.77 1203138 6 o=[];
0.68 1203138 7 dfdu=[];
1.16 1203138 8 dfdp=[];
9
130.77 1203138 10 o=feval('ab',0,u,par(1:3),'outputs');
122.66 1203138 11 f=feval('ab',0,u,par(1:3),'derivs');
12
0.51 1203138 13 u1=u(1);
0.51 1203138 14 u2=u(2);
15
0.97 1203138 16 e=double(exp(u2));
17
0.52 1203138 18 f(1)=-u1 + par(1)*(1-u1)*e;
3.42 1203138 19 f(2)=-u2 + par(1)*par(2)*(1-u1)*e - par(3)*u2;
From: Steven_Lord on 3 Aug 2010 16:37


"Etienne" <etienne.coetzee(a)airbus.com> wrote in message
news:i2t5ir$15f$1(a)fred.mathworks.com...
> Hi Folks
>
> I am trying to calculate the derivatiaves of a function. However, when I
> implement the equations in a matlab function, and then in a simulink
> function, the simulink model runs a lot slower. I ran the profiler and
> get the results at the end of the message. Line 11 does the same as 18 and
> 19. Why the massive difference? I have disabled the simulink autosave
> function, checked for writing to the workspace etc, but I am not sure if
> there might be other simulink settings I can try.
>
> Thanks
>
> Etienne
>
> ===============================================
> time calls line
> 1 function [f,o,dfdu,dfdp]=absimfunc(par,u,ijac)
> 2 %
> 3 % function file for demo ab
> 4 %
> 1.11 1203138 5 f=[0,0]; 0.77 1203138 6 o=[]; 0.68 1203138
> 7 dfdu=[]; 1.16 1203138 8 dfdp=[]; 9 130.77 1203138 10
> o=feval('ab',0,u,par(1:3),'outputs');

Do NOT call your function using FEVAL. You _know_ what function you're
calling -- so just call it!

o = ab(0, u, par(1:3), 'outputs');

> 122.66 1203138 11 f=feval('ab',0,u,par(1:3),'derivs');

Ditto on the FEVAL.

This also renders line 5 unnecessary, unless line 10 can somehow prematurely
return from the function.

> 12 0.51 1203138 13 u1=u(1); 0.51 1203138
> 14 u2=u(2); 15 0.97 1203138 16 e=double(exp(u2)); 17 0.52 1203138
> 18 f(1)=-u1 + par(1)*(1-u1)*e; 3.42 1203138 19 f(2)=-u2 +
> par(1)*par(2)*(1-u1)*e - par(3)*u2;

Note that lines 18 and 19 are overwriting the f that you created on line 11
[assuming that the output of line 11 is a 2-element vector] so line 11 is
dead code (unless your ab function has a side effect that occurs as a part
of its execution, like writing to a file or creating graphics.)

--
Steve Lord
slord(a)mathworks.com
comp.soft-sys.matlab (CSSM) FAQ: http://matlabwiki.mathworks.com/MATLAB_FAQ
To contact Technical Support use the Contact Us link on
http://www.mathworks.com

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