MATLAB: Finding specific values in a function

functionminminimumplotvector

So i have a function f(x) and it is basically a curve. I am trying to find the point on in then the curve is at its minimum. To find the y coordinate i just used min(f(x)). My question is how do I find the x value that corresponds to that. x is a vector of about 100 terms if that makes a difference. The function is kind of long and complicated or else I would just solve for x. Is there a command that will give me that matching x value to the y minimum? Thank You.

Best Answer

[y, yidx] = min(f(x));

Then x(yidx) is the x that evaluates to the minimum.

Related Solutions

MATLAB: I want to find the x and y values of f(x,y) when f(x,y) is a minimum over x = -1:0.001:1 and y = -1:0.001:1.

x=-1:0.001:1
y=x
[ii,jj]=ndgrid(x,y]
z=sin(ii)+cos(jj)   % Example
[min_val,index]=min(z)
xidx=x(index)
yidx=y(index)

MATLAB: Display the x value of a graph knowing the y value

Supposing you had done

plot(x,y)

and that the value you are looking for is ProbeY (an arbitrary variable name)

[ydist, yidx] = sort(abs(y - ProbeY));

Then

x(yidx(1))

is the x for which y(x) is the closest to ProbeY.

Sometimes, though, you only want locations where y(x) is at most ProbeY

ylocs = find(ProbeY >= y);
[ydist, ylocsidx] = sort(ProbeY(ylocs)-y);
closestyidx = ylocs(ylocsidx(1));

and then x(closestyidx) is the x for which y(x) is closest to but does not exceed ProbeY.

Best Answer

Related Solutions

MATLAB: I want to find the x and y values of f(x,y) when f(x,y) is a minimum over x = -1:0.001:1 and y = -1:0.001:1.

MATLAB: Display the x value of a graph knowing the y value

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