Is it possible to fit a*x**b + c?

[lesshaste]

I would like to perform a least-squares fit to a curve. I tried

a, b,c  = parameters('a, b, c')
x = variables('x')
model = a*x**b + c

However symfit complains about the exponentiation with

AttributeError: 'Tuple' object has no attribute '_eval_power'

Is this possible to do in symfit?

[pckroon]

Yes, but variables returns a tuple (of Variables). Two solutions:

a, b,c  = parameters('a, b, c')
x, = variables('x')  # Note the extra comma
model = a*x**b + c

or

x = Variable('x')

[lesshaste]

Thank you so much.