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curve fitting coefficients.

asked 2016-01-04 12:36:40 -0500

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get the model coefficients, but I can not use them to plot the graph. How to solve?

see the code:

dados = [(0, -0.183440428023042),
 (0.200000000000000, -0.131101157495126),
 (0.400000000000000, 0.0268875670852843),
 (0.800000000000000, 0.110532679260319),
 (1.00000000000000, 0.253944632998395),
 (1.20000000000000, 0.257190123748649),
 (1.40000000000000, 0.531888837111346),
 (1.60000000000000, 0.579048247883555),
 (2.00000000000000, 0.935180993484717),
 (2.20000000000000, 0.916600344376623),
 (2.60000000000000, 1.13328608090532),
 (2.80000000000000, 1.26893326843583),
 (3.00000000000000, 1.10202945535186),
 (3.40000000000000, 1.13391615491257)]

point(dados,color = "red",size=20,legend_label="pontos coletados")

modelo(x) = a*x+b;modelo

a,b = find_fit(dados, modelo);a;b

modelo(x) = a*x+b

point(dados,color = "red",size=20,legend_label="pontos coletados") + plot(modelo(x),(x,0,3))
Traceback (click to the left of this block for traceback)
...
ValueError: Variable 'x' not found
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What are 'a' and 'b'? Did you define them as variables?

vdelecroix gravatar imagevdelecroix ( 2016-01-04 13:42:43 -0500 )edit

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answered 2016-01-04 13:46:39 -0500

You should do

sage: a,b = var('a', 'b')
sage: modelo(x) = a*x+b
sage: print modelo
x |--> a*x + b
sage: d = find_fit(dados, modelo, solution_dict=True)
sage: print d
{b: -0.1757321718542446, a: 0.4599622663189693}
sage: modelo2 = modelo.subs(d)
sage: print modelo2
x |--> 0.4599622663189693*x - 0.1757321718542446
sage: point(dados,color = "red",size=20,legend_label="pontos coletados") + plot(modelo2,(x,0,3))

In your code, the variable does not get substituted as expected. You can see it by printing what is modelo.

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hello vdelecroix Thank you for your help ;). Now it works correctly.

jmarcellopereira gravatar imagejmarcellopereira ( 2016-01-04 16:00:43 -0500 )edit

@jmarcellopereira De nada! If you are satisfied with my answer, you can select it with the check box that appear on its left ("mark this answer as correct"). That way this question will appeared as "solved" in the list of questions.

vdelecroix gravatar imagevdelecroix ( 2016-01-04 19:28:51 -0500 )edit

marked ;)

jmarcellopereira gravatar imagejmarcellopereira ( 2016-01-04 20:49:14 -0500 )edit

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Asked: 2016-01-04 12:36:40 -0500

Seen: 102 times

Last updated: Jan 04 '16