Linear Exponential Combination Fit

[Albert Chan]

Hi, Eddie

Thanks for the post. I did not know HP Prime had LSQ function.

It might be simpler not to create a flatten list (with CONCAT), then reconstruct the matrix.
We could build the matrix, functional style:

CAS> lx := range(6)
CAS> ly := [2, 7, 13, 18, 26, 34]
CAS> fit := LSQ(transpose([0*lx .+ 1., lx, e^lx]), ly)

[[1.74935499144],[5.39455446221],[3.66584105036e−2]]

CAS> [[1,x,e^x]] * fit

[[ 3.66584105036E−2*e^x + 5.39455446221*x + 1.74935499144 ]]

Comment: Aug 21, 2023

".+" is supposed to apply sum element-by-element.

However, XCas (lx-lx) .+ 1. does not populate matrix with all one's, (0*lx .+ 1.) does.
To bypass the bug, above is adjusted so that both CAS, XCAS produce same results.

Also, if we only need polynomial regression, there is a shortcut

polynomial_regression(lx, ly, degree_needed)