Creating a for loop based on a condition

Hello everyone, I need to create a for loop which iterates until it is met a specific condition, which in my case is the output being equal to a certain value. I know a while loop would suffice, though I would require a for-loop in order to use the index of the iteration to store the output of said iteration into an array, so that I can have a full accountability of all the results the loop gets.

[Dyuman Joshi]

Use break or return.

Answer 1

[Walter Roberson]

for K = 1 : inf
    do some calculation
    stored_results(K) = the_output
    if the_output == the_certain_value
        break;
    end
end

or

K = 0;
while true
    do some calculations
    K = K + 1;
    stored_results(K) = the_output;
    if the_output == the_certain_value
        break;
    end
end

However... remember that the == operator is looking for bit-for-bit equality, and it is possible that you cannot get bit-for-bit equality due to round-off and finite precision . You are typically better off checking to see whether the output is "close enough" to the desired value, such as with ismembertol()

Answer 2

[Torsten]

i = 0;
tolerance = 1e-4;
imax = 100;
output = 1;
value = ...;
while abs(output-value) > tolerance && i < imax
    i = i + 1;
    ...  % compute something
    output = ...;
    OutputArray(i) = output;
end
plot(1:i,OutputArray)