How can I solve a function for x given y?

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.

Answer 1

[Matt J]

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

[Kait Clark]

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]

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]

Ahhh makes sense! That did it! THANK YOU!

[Matt J]

Or give the interval of interest for x, e.g.,

x=fzero(@(x) f(x)-0.77, [0,0.25])