CODEWITHSUNDEEP
matlabloopswhile-loopstore
Scott
Scott

Reputation: 63

Storing values with a while loop (matlab)

I have a while loop and I've been unable to determine how to store the values successfully. Any help would be greatly appreciated. 

n = 0; a = 21; b = 0; c = 0; y = 37.6991; T = 18.5; z = 0.1591; d = 0; f = 15.3049; q = 2.2391e4; e = 5; x = 60;  
while n < x
        a = a + b                 
        c = y*(T-a)/z;                   
        d = f*c;              
        b = d/q;                  
        n = n + e; 
    end

The value I'm trying to store is a, I can tell the values are correct inside the loop but just can't seem to store the values correctly.

Upvotes: 0

Views: 707

Answers (2)

stephematician
stephematician

Reputation: 884

Another approach would be to recognise that it is a relatively simple recurrence relation:

n = 0; a = 21; y = 37.6991; T = 18.5; z = 0.1591; f = 15.3049; q = 2.2391e4; e = 5; x = 60;
while n < x
    a(end+1) = a(end) + f * y * (T - a(end)) / (q * z);
    n = n + e;
end

This calculation can also be vectorised, but if you want exactly the same output you need to be a little bit careful:

n  = 5:5:55; y = 37.6991; T = 18.5; z = 0.1591; f = 15.3049; q = 2.2391e4; a0 = 21;
alpha = f * y * T / (q * z);
beta  = (1 - f * y / (q * z)).^(0:length(n))

a = a0 * beta + alpha * [0 cumsum(beta(1:end-1))];

The code seems to lose clarity (to me) when vectorised, so I would probably prefer the loop in this scenario.

Upvotes: 1

itzik Ben Shabat
itzik Ben Shabat

Reputation: 927

Try this : 

counter = 1;
n = 0; a = 21; b = 0; c = 0; y = 37.6991; T = 18.5; z = 0.1591; d = 0; f = 15.3049; q = 2.2391e4; e = 5; x = 60;  
var = zeros(1,12);
while n < x
        a = a + b;                 
        c = y*(T-a)/z;                   
        d = f*c;              
        b = d/q;                  
        n = n + e; 
        var(counter) = a;
        counter = counter+1;
end

I added a variable called var which is a vector that stores the values of a. In order t osave runtime i initialized it to the expected size of the variable var = zeros(1,12); (This is not strictly required but is recommended.

Upvotes: 0

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