MATLAB: There is no update of variables, if I iterate them in for-loop !

for loop iteration errorif else loop errorMATLAB

My 'eps_new', 's_new' values in the following matlab code is not updating itself and I get an error saying ''index exceeds no. of array elements (1)'' even though I iterate it over for-loop.

Thank You in advance.

eps_new=[0.00978536954672866];
s_new=[351.487914254540];
n=zeros;
dsn=zeros;
alfa_n=zeros;
for j=1:400
   if s_new<0  
alfa_n(j)=-1*((2/3)*(c/h)+(abs(s_new(j))-(2/3)*(c/h))*exp(-h*(abs(eps_new(j)))));
    else
alfa_n(j)=((2/3)*(c/h)+(abs(s_new(j))-(2/3)*(c/h))*exp(-h*(abs(eps_new(j)))));
   end
alfan(j)=alfa_n(j);
s_kln(j)=s_new(j)-((1/3)*s_new(j));
if s_kln<0
f1n(j)=abs((sqrt((-3/2)*(s_kln(j)-alfan(j))^2))-((366.772-187.398)/(0.010319-0.0010619))-192.098);
else
f1n(j)=abs((sqrt((3/2)*(s_kln(j)-alfan(j))^2))-((366.772-187.398)/(0.010319-0.0010619))-192.098);
end
    dln(j)=f1n(j)/((df_ds*E)+c+h);
    d_eps_pn(j)=dln(j)*df_ds;
    
    n(j+1)=d_eps_pn(j)+eps_new(j);
    
    if 0.00473>n>0.0103
        eps_new(j+1)=eps_new(j)-d_eps_pn(j);
    else
        eps_new(j+1)=eps_new(j)+d_eps_pn(j);
    end
    
    
    
    if 0.0068985>eps_new>0.010319
        dsn(j)=R*(d_eps_pn(j));
        s_new(j+1)=s_new(j)+dsn(j);
    elseif 0.0047328>eps_new>0.0082064 
        dsn(j)=R*(d_eps_pn(j));
        s_new(j+1)=s_new(j)+dsn(j);
    elseif 0.0082064>eps_new>0.010319
        dsn(j)=-E*(d_eps_pn(j));
        s_new(j+1)=s_new(j)+dsn(j);
    elseif 0.0047328>eps_new>0.0068985
        dsn(j)=E*(d_eps_pn(j));
        s_new(j+1)=s_new(j)+dsn(j);
    end
 
end

Best Answer

 if s_new<0

For MATLAB that means the same thing as

if all(s_new<0)

That is important because you are adding additional elements to the vector in the loop.

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MATLAB: MATLAB code never stops running (infinite loop)

Around line 62 or so you have

for n=1:now

Within that for loop, around line 140 or so you have

                 if m ==1
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                                Permf(n,i)=P(j,i);
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                        end
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Notice that you have the for n inside the for n . MATLAB does define what happens when you do this: the change to n will be in effect until the next outer for n starts, at which point n will be set to the "next" value of the outer loop as-if the change to n had not been done. But meanwhile until the bottom of the loop, n has changed. In particular at your line just inside the inner while loop you are having problems with,

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the n that is going to be used there is the n that was left-over from the inner for n loop, not the n associated with the outer for n loop.

Notice as well that the assignment to Permf is inside a triple for loop but is assigning to a variable using only two indices. The value that Permf(n,i) is going to be left with is going to be the last value assigned to it. You could achieve the same effect with

Permf(1:now, 1:noc) = P(nos, 1:noc)

and since you are not initializing Permf (growing it inside the loop) and it is always the same size, this in turn could be expressed as

Permf = repmat(P(nos, :), now, 1);

with no loop.

Are you sure that is what you want Permf to be assigned?

Any time you have a for loop that is not doing reduction (e.g., totaling the P values) and has more nesting levels than the number of indices of the output variable, then you should be optimizing to do only what would be left in the final result after the overly-nested assignments were complete.

MATLAB: Problem in while loop

You should be using

b(:,j) = V(:,j)

not n in your loop, which also should probably be a for loop, but that's a side issue - a while still works. And obviously all the other places you are using n instead of j too

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