# Using fzero to find variation

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Alex Innes on 28 Sep 2020 at 21:37
Answered: Walter Roberson on 29 Sep 2020 at 1:15
Use fzero to determine by how much the value of D can vary from it’s optimal value before the tension increases by more than 10% from it’s minimum, and display this value in the Command Window.(this is what I need to accomplish)
I have already written the rest of the program that gives me the optimal value D and the value of the tension while using a anonymous function. Not sure how to exactly go about using fzero in order to find the max variation of D.

Walter Roberson on 29 Sep 2020 at 1:15
If you know the optimal D and optimal tension, and you have a function that calculates tension given D, then if you find the zeros of
calculate_tension(optimal_D-deltaminus)-.9*tension
calculate_tension(optimal_D+deltaplus) - 1.1*tension
then deltaminus and deltaplus are the values being asked for.

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