Is there an alternative to Eval() ? - Large equation in a text file needs to be evaluated in Simulink

Hello,

I have a large text file (>150MB)as a result of a symbolic calculation that includes elements of a matrix in the form of:

    A(i)= ...; (where i=1,2,...,15)

I created a Simulink block that runs a C Mex S-function to evaluate the matrix from the text file. I need the Simulink model to design a controller for a mechanical system.

The method I am using right know is solely based on "eval()" that is included in a Matlab function which is called by "mexCallMATLAB()" from the S-function. This is very inefficient timewise.

Another method I tried was converting the Matlab code into C code using built-in "ccode()" function. This would have been ideal to use in a C Mex S-function. In this case, however, maple generated too many intermediate variables which I thought was hard to keep track of and eliminated this option.

I would like to learn if there is a better way of handling this kind of a scenario in terms of reduced time for that block to produce results. Thank you for your comments/suggestions in advance.

Regards,

Ernur Karadogan

Answer 1

[Walter Roberson]

In Maple, did you try

codegen[C](Expression,optimized)

Though the optimized option will introduce many more intermediate variables than if you do not optimize.

Is your Maple new enough to use

CodeGeneration[Matlab](Expression)

The expression can be followed by optimize=true or optimize=tryhard though either one might make the code harder to follow.

[Ernur]

Walter,

Thank you for your suggestion, but I don't have access to Maple directly.

Ernur

[Walter Roberson]

You mention "maple" in one place -- was that a typo ?

[Ernur]

No. Matlab's "ccode()" function generates those intermediate variables by using Maple.

[Walter Roberson]

Which version are you using? Since about 2008, MuPad would be used instead of Maple. If you are using a 2007 or earlier version, then I _suspect_ you could get the access to the Maple code generation functions, but I am not certain (I don't have the toolkit to try with.)

If you are using a newer version that uses MuPad, have you considered using matlabFunction() ?

[Ernur]

Walter,

Sorry for the late reply. I am using version 2006b. It seems that I should think about upgrading. Thanks for your time.

Ernur

Answer 2

[Ernur]

I was able to reduce the time significantly by dividing the text file into manageable chunks and using the following instead of "eval()":

file_name_Source = sprintf('src_file_path.txt',var1,var2,...);

file_name_Destination =sprintf('dest_file_path.m',var1,var2,...);

copyfile(file_name_Source,file_name_Destination);

run(file_name_Destination);

Remarks:

1) After this modification, the elapsed time for two time steps (including t=0) in Simulink reduced by 96% as compared to the scenario with "eval()" (from 576sec to 22sec).

2) I used "sprintf()" to loop through all files which may not be necessary for another case,

3) If you would like to use this method, you could write your output/save with an .m extension so that you don't have to use the "copyfile()" function.

[Walter Roberson]

Or you could just rename the .txt files ;-)