Solving for an x value using ppval

Question

David Hagan 2012-1-3

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https://ww2.mathworks.cn/matlabcentral/answers/25179-solving-for-an-x-value-using-ppval

I have created a linear piecewise function using interp1 which works beautifully given the x value. Is there a way for which I could solve for an x value given the Y value? Example:

 hotStreamInterp = interp1(B,Hhotpt, 'linear', 'pp')';
 x = fsolve(480 = ppval(hotStreamInterp, x_unknown));

How could I properly write this? Thank you.

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Answer 1

Andrew Newell 2012-1-3

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It depends - if x and y are 1-1, you can just switch them in the above two lines. In general, however, there is probably more than one x value for a given y value. Then you'll have to decide whether you want x from a particular interval or all the values of x. If you know where the extrema in x are, you could interpolate in the intervals between extrema.