MATLAB: Converting Fortran to MATLAB

fortrangotoifiterationMATLABnested loopsrecurrencewhile

Greetings, all

I have found a powerful yet compact Fortran code which I am trying to reprogram into MATLAB. Unfortunately, I have now hit a point where I need some help with the logic. The algorithms are easy enough to convert, so I'm not going to show them (unless you really want me to).

My problem is converting the Fortran "GOTO" logic into MATLAB. I have decided to study the sequence in which things happen, and from this created a map of triggers (e.g. if…goto 23 (else) goto 13) and I need to design my loops and functions around these. Some are simple enough (those in the green frames), but one of them (red frame) really has me baffled…

The nested loop between 15 and 19 is just three "for" loops, which are easily coded but less easily illustrated here. They are terminated by 16, 17 and 18 repectively.

From 28 on the calculations are done and some sequential post-processing takes place.

Thanks in advance

Best Answer

Use "continue" to resume back at point #13. Continue ends the current iteration of the enclosing loop and starts the next iteration.

Matters would be slightly more complicated if you needed to break out of the nested loops and go back to #13, but you do not need to do that so don't worry about it ;-)

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MATLAB: While loop with power.

This is the discrete logarithm problem.

https://en.wikipedia.org/wiki/Discrete_logarithm#:~:text=Modular%20arithmetic.%20One%20of%20the%20simplest%20settings%20for,of%20the%20elements%20followed%20by%20reduction%20modulo%20p.

In general, there is no simple solution, but using a while loop seems a poor choice. There is a list of better schemes available, but nothing trivially written. Do some reading based on the links on the wiki page. For example...

https://en.wikipedia.org/wiki/Pollard%27s_rho_algorithm_for_logarithms

But no. You don't want to use a while loop. That would be a bad idea. There is no tool in the symbolic toolbox for this purpose, nor is there a tool I have written in my toolboxes. It looks like the worse case will probably arise when N is a prime.

MATLAB: Having Fun Yet

When I check the MATLAB 5.0 (release 10) documentation it says that pack works by saving the workspace to a file, clearing all functions and variables from memory, and loading the file.

If it were executed from a function or script then it would clear the function or script from memory, destroying what it was executing. Especially if it was a function, since it is not the current workspace that is saved, just the base workspace.

So you have code that blows itself out of the water and you are upset that current versions have no

feature('allowcodetocorruptitself', true)

... Or do I need to try find even older release documentation?

Best Answer

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MATLAB: While loop with power.

MATLAB: Having Fun Yet

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