Given a function and x limits of a function, how do I divide y-coordinates of a function in set increments?

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soloby 2015-6-4

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关闭： MATLAB Answer Bot 2021-8-20

for example,

x = -20:0.4:20; f1 = gaussmf(x, [2 2]);

I am working on fuzzy operations so I need to get the lower and upper bounds of x for incremental values of y, for example, if my y is 0 to 1 i need each x-values of y from 0, 0.01, 0.02.. ..0.99, 1

what's the best way to get the x-values? find() doesn't work because matlab already assigns f1 101 values that's not in increments of 0.01

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Answer 1

Star Strider 2015-6-4

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It depends on the nature of your function. You could use a generic regression function such as polyfit or an interpolation function such as interp1, with the x and y arguments reversed from the usual order, since you want the x values for certain values of y.

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soloby 2015-6-4

this looks very promising, I just have a couple of questions, is there a way i can apply this to the gaussmf(x, [2 2]) function directly? and why did you choose alpha to be .95? I assume it's arbitrary.

thanks very much for your help

Star Strider 2015-6-4

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My pleasure.

To apply it to gaussmf(x,[2 2]) directly, you would have to calculate its inverse. The easiest way to do that is with the fzero function. You would have to do that in a loop, but you would only have to do it for values of x<=2, and create a symmetric vector with values for x>2.

To calculate the x for a particular y, try this:

sig = 2;
c   = 2;
invgaussmf = @(x,y) gaussmf(x, [sig c])-y;              % Inverse Function
N = 10;
y = linspace(1E-4, 1-1E-4, N);                          % Vector Of ‘y’
for k1 = 1:N
    x = fzero(@(x) invgaussmf(x,y(k1)), 0.5);
    mf(k1,:) = [y(k1)  x];                              % [y x] Matrix
end

You will probably have to experiment with it to get the result you want. You might want to plot y as a function of x to be sure it’s doing what you want.

Given a function and x limits of a function, how do I divide y-coordinates of a function in set increments?

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