How to multiply 3 matrices?

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subha
subha 2014-8-19
编辑： subha 2014-8-21
I want to multiply 3 matrix. each has dimension sigmas=1*784, poshidstates=100*500, vishid=784*500. Then i want to add this with matrix of dimension visbiases=1*784. numdims=784,numcases=100.
i have done this as,
negdatapart=repmat(sigmas,numdims,1)' *(poshidstates*vishid')' ;
negdata= negdatapart'+repmat(visbiases,numcases,1)
something goes wrong here i guess. Can someone give me an idea
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subha
subha 2014-8-19
编辑：subha 2014-8-19
@Michael- I want to represent this equation. visbias+sigmas(poshidstates*vishid).
Dimensions are mentioned in the question. I want to get negdata variable to have dimension 100*784. I too guess the problem is with sigmas only. Because if i remove sigmas and write as below, my program works good( that is, i was able to see the output. Otherwise values are getting NAN after few iterations. ). I believe this is because of this two statements. Inparticular because of sigma. i removed sigma and run. It was working fine
negdatapart= vishid*poshidstates'
dpb
dpb 2014-8-20
As others have suggested, you need to back off to a small-enough problem that you can compute the correct answer and then use debug to work thru the logic error in where it goes wrong. That it's "after a few iterations" probably means a logic error elsewhere as if it were a dimensions problem as has been pointed out, it wouldn't work at all.
IOW, as another has also suggested, what you apparently have is a logic error, not Matlab-specific error and you need to see why the result begins to deviate to follow where it goes wrong. That again is probably practical only w/ a very small problem sample size instead of order of 100's.

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Matt J
Matt J 2014-8-19
编辑：Matt J 2014-8-19
negdata=bsxfun(@plus, sigmas+visbiases, poshidstates*vishid')
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Matt J
Matt J 2014-8-20
编辑：Matt J 2014-8-20
mult_result=bsxfun(@times, sigmas, poshidstates*vishid');
add_result=bsxfun(@plus, visbiases, mult_result);
If this istill sn't precisely what you want, you should still be able to figure it out from the documentation from bsxfun. It's generally what you would use for any kind of element-wise operation between a matrix and a vector.
subha
subha 2014-8-21
编辑：subha 2014-8-21
Hi matt,
Thanks. I just found this answer and came to post the answer. You have given already.. Its working proper. This is the perfect answer

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