How do i replace this code to fast up?

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subha
subha on 25 Aug 2014
Answered: Iain on 29 Aug 2014
Variable poshidstates have 4 possible values(0,1,2,3). Everytime, poshidstates has to select 1 value out of this four.In this below code, i=100,j=500. Because of below mentioned code part , my program run more than 8 hour instead of just 1 hour(I have to call this code for 600 batches and each batch for 50 times). how can i replace this?
val_vect=[0 1 2 3];
for i=1:numcases;
for j=1:numhid;
prob=[poshidprobs0(i,j),poshidprobs1(i,j),poshidprobs2(i,j),poshidprobs3(i,j)];
K=find(mnrnd(1,prob)==1);
poshidstate(i,j)=val_vect(K);
end
end
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Iain
Iain on 28 Aug 2014
Ok, now I see why it takes so long. You're repeating that calculation 30,000 times.
But seeing what you're doing, this might be faster:
temp = rand(100, 500);
poshidstate = (temp > poshidprobs0) + (temp > (poshidprobs0 + poshidprobs1)) + (temp > (poshidprobs0 + poshidprobs1 + poshidprobs2));
subha
subha on 28 Aug 2014
Edited: subha on 29 Aug 2014
Hi lain, Thanks a lot..I am so happy. You saved lots and lots of time .Problem resolved. I am searching for this for long. Now its just take 40 minutes. Thank u so much.No words to express.So happy. Please post this as answer. So many will be looking for this. Thanks mathworks

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Accepted Answer

Iain
Iain on 29 Aug 2014
Ok, now I see why it takes so long. You're repeating that calculation 30,000 times.
But seeing what you're doing, this might be faster:
temp = rand(100, 500);
poshidstate = (temp > poshidprobs0) + (temp > (poshidprobs0 + poshidprobs1)) + (temp > (poshidprobs0 + poshidprobs1 + poshidprobs2));

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