## scipy.optimize.curve_fit: not a proper array of floats error

Question

I'm trying to use optimization.curve_fit to find the least square solution between two arrays, but I keep getting error: Result from function call is not a proper array of floats. I pasted my code below. Any ideas how to fix this? Thank you!

``````import numpy as np
import scipy.optimize as optimization

pcone = np.array([[-0.01043151],
[-0.00135030],
[-0.02566969],
[-0.02822495],
[-0.05463625],
[-0.00969918],
[-0.01332421],
[-0.03364439],
[-0.04009642],
[-0.03556982]])

pctwo = np.array([[0.02550008],
[0.04422852],
[0.06685288],
[0.04751296],
[0.02439405],
[0.09654185],
[0.03161849],
[0.03834721],
[0.01653997],
[-0.00802414]])

def func(x, a, b, c):
return a   b*x   c*x*x

print optimization.curve_fit(func, pcone, pctwo)
``````
Solution

Your arrays have shape (10, 1). That is, they are two-dimensional, with a trivial second dimension. In the simplest case, `curve_fit` expects one-dimensional arrays. Flatten `pcone` and `pctwo` into one-dimensional arrays before passing them to `curve_fit`.

For example, this works:

``````In : curve_fit(func, pcone.ravel(), pctwo.ravel())
Out:
(array([ 0.05720879,  0.65281483, -2.67840575]),
array([[  5.90887090e-04,   4.15822858e-02,   6.14439732e-01],
[  4.15822858e-02,   4.07354227e 00,   6.94784914e 01],
[  6.14439732e-01,   6.94784914e 01,   1.29240335e 03]]))
``````

(You haven't shown how `pcone` and `pctwo` were created. It would probably be cleaner to create them as 1-D arrays in the first place, instead of flattening them later.)