#13772: find_fit doesn't work when function with substituted initial_guess
parameters and independent variable from data contains fractional power of
a negative number
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Reporter: infroma | Owner: jason, jkantor
Type: defect | Status: new
Priority: major | Milestone: sage-5.6
Component: numerical | Keywords:
find_fit,initial_guess,wrong,fractional power,negative number
Work issues: | Report Upstream: N/A
Reviewers: | Authors:
Merged in: | Dependencies:
Stopgaps: |
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Sometimes user's initial_guess can lead to fractional power of a negative
number on some substituted independent variable from "data"
variable.[[BR]][[BR]]It happend to me, when I wanted calculate diode's
parameters. I know approximate diode parameters and I pass them as
initial_guess, but get error. Of course, I can try to select other values
until ending of errors, but it isn't cool.[[BR]][[BR]]Simple code to
illustrate:
{{{
#!python
def f(x, q):
return sqrt(x - q)
var('q')
a = [[5, 2], [10, 3], [17, 4], [26, 5]] # it's y = sqrt(x - 1)
M = Matrix(a)
five = 4.9999999 # Calculated normally, solution ~= 1
#five = 4.99999999 # Fails
find_fit(M, f, parameters = [q], variables = [x], initial_guess = [five])
# this works correctly with the same initial guesses, when it fails, it
returns initial guess as a result
model(x) = sqrt(x - q)
find_fit(M, model, initial_guess = [5])
}}}
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13772>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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