MATLAB: Matlab interp1 function x-points for given y-points

interp1interpolation

Dear Community Members,
Hopefully this finds you safe and well. Using interp1 to acquire x-points for given y-points does not seem to work. Data in this particular instance generated via a function however in reality it is experimental data.
%**main function
x=[3:0.1:6];
y=sin(x);
%***y-array for new x-values
y_array = [-0.9:0.005:0.1];
x_new = interp1(y,x,y_array);
figure
plot(x,y,'k+-',x_new,y_array,'rx-')    
grid on
Resutant image see attachment.
Any help on how to extrapolate between current and next data opints would be appreciated.

Best Answer

Inverting nonlinear function using interp1() like this is not correct. Check the following code
%**main function
x=[3:0.1:6];
y=sin(x);
%***y-array for new x-values
y_array = -0.9:0.005:0.1;
interp_x = @(xq) interp1(x, y, xq);
x_new = fsolve(@(xq) interp_x(xq) - y_array, 3+rand(size(y_array)));
figure
plot(x,y,'k+-',x_new,y_array,'rx-')    
grid on
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