Errors in Vectorized For-loop Matlab Code

0
votes

I have a for loop code which I want to vectorize. Below is the initial for loop code, and the vectorized version of the code. The vectorized code isn't giving the same result as that of the parfor loop, hence I know something is wrong with the code. I would appreciate it if any member of the forum can help me review the vectorized code and see if they can point out my errors to me. Thank you in advance.

% Initialization and precomputations % w is an n x 1 vector % beta: any number larger than 0. Usually set to 1. Here is the for-loop code I need to vectorize:

f = zeros(n,1);
x = w;
y = w;
rho = 1;
v = f – (rho*y);
rhow = rho*w;
n = length(w);

parfor i = 1 : n

if w(i) >= 0
    if v(i) < -rhow(i) – beta – 1
        x(i) = (-beta -1 -v(i))/rho;

    elseif (-rhow(i) – beta – 1 <= v(i)) && (v(i) <= -rhow(i) + beta – 1)
        x(i) = w(i);

    elseif (-rhow(i) + beta – 1 < v(i)) && (v(i) < beta – 1)
        x(i) = (beta – 1 -v(i))/rho;

    elseif (beta – 1 <= v(i)) && (v(i) <= beta + 1)
        x(i) = 0;

    else
        x(i) = (beta + 1 – v(i))/rho;
    end

else

    if v(i) < -beta -1
        x(i) = (-beta -1 – v(i))/rho;

    elseif (-beta – 1 <= v(i) )&& (v(i) <= -beta + 1)
        x(i) = 0;

    elseif (-beta + 1 < v(i)) && (v(i) < -rhow(i) – beta + 1)
        x(i) = (-beta + 1 – v(i))/rho;

    elseif (-rhow(i) – beta + 1 <= v(i)) && (v(i) <= -rhow(i) + beta + 1)
        x(i) = w(i);

    else
        x(i) = (beta + 1 – v(i))/rho;
    end

end

end

======================================================================

And here is my vectorized version of the code above: 

cond1 = (w >= 0);
cond2 = (w >= 0) & (v < -rhow-beta-1);       
x(cond2) = (-beta-1-v(cond2))/rho; 

cond3 = (w>=0)&(-rhow - beta -1 <= v) & (v <= -rhow + beta - 1);
x(cond3) =  w(cond3);

cond4 = (w>=0) & (-rhow +beta - 1 < v) & (v < beta - 1);
x(cond4) = (beta - 1 - v(cond4))/rho;

cond5 = (w>=0) & (beta - 1 <= v) & (v <= beta + 1);
x(cond5) = 0;

cond6 = (~cond2);
x(cond6) = (beta + 1 - v(cond6))/rho;

cond7 = ((~cond1) & v < -beta -1);
x(cond7) = (-beta -1 - v(cond7))/rho;

cond8 = ((~cond1) & (-beta - 1 <= v) & (v <= -beta + 1));
x(cond8) = 0;

cond9 = ((~cond1) & (-beta + 1 < v) & (v < -rhow - beta + 1));
x(cond9) = (-beta + 1 - v(cond9))/rho;

cond10 = ((~cond1) & (-rhow - beta + 1 <= v) & (v <= -rhow + beta + 1));
x(cond10) = w(cond10);

cond11 = (~cond1);
x(cond11) = (beta + 1 - v(cond11))/rho;
2
matlabif-statementfor-loopparfor

2 Answers

0
votes

I'm adding another answer with all the conditionals checked:

cond1 = (w >= 0);
cond2 = cond1 & (v < -rhow – beta – 1);
cond3 = cond1 & ((-rhow – beta – 1 <= v) && (v <= -rhow + beta – 1));
cond4 = cond1 & ((-rhow + beta – 1 < v) && (v < beta – 1));
cond5 = cond1 & ((beta – 1 <= v) && (v <= beta + 1));
cond6 = cond1 & (v > beta + 1)

cond7 = ~cond1 & (v < -beta -1);
cond8 = ~cond1 & ((-beta – 1 <= v ) && (v <= -beta + 1));
cond9 = ~cond1 & ((-beta + 1 < v) && (v < -rhow – beta + 1));
cond10 = ~cond1 & ((-rhow – beta + 1 <= v) && (v <= -rhow + beta + 1));
cond11 = ~cond1 & (v > -rhow + beta + 1);

x(cond2)=... to x(cond11)=... remain the same. Hope this works.

0
votes

Here is one mistake, cond6 is not equivalent to the original first else

cond2 = (w >= 0) & (v < -rhow-beta-1);
cond6 = (~cond2);
x(cond6) = (beta + 1 - v(cond6))/rho;

in the original this is:

if w(i) >= 0
   if v(i) < -rhow(i) – beta – 1
      ...
   else
      x(i) = (beta + 1 – v(i))/rho;  %this should be cond6
   end
end

The else should be evaluated like this (If I'm not mistaken)

x(cond1) = (beta + 1 - v(cond6))/rho;

and before all the others up to cond5.

I did not check all the code, so if this doesn't solve your problem let me know.