How can I solve a function for x given y?

2020 10 8
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更新时间：2020 10 8
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I am trying to solve the following Weibull function for x given y.
f=fit(edges, binMean, 'Weibull', 'StartPoint', [0.01, 2]);
Obviously it's easy to solve for y given x.
y=f(0.77)
But how can I do the reverse? I want to know x when y is 0.77.

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Matt J
Matt J 2020-10-8

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x=fzero(@(x) f(x)-y, 0.5 )

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Kait Clark
Kait Clark 2020-10-8
Thanks Matt. Just tried this as
x=fzero(@(x) f(x)-0.77, 0.5 )
but it gave me 0.6332
This doesn't appear to work as the correct value is about 0.07.
Walter Roberson
Walter Roberson 2020-10-8
The equation curves downwards later and 0.6332 is another root.
Give a different starting guess, such as
x=fzero(@(x) f(x)-0.77, 0.1 )
Kait Clark
Kait Clark 2020-10-8
Ahhh makes sense! That did it! THANK YOU!
Matt J
Matt J 2020-10-8
Or give the interval of interest for x, e.g.,
x=fzero(@(x) f(x)-0.77, [0,0.25])

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