[SciPy-user] plot curve of a series of equations

Gary Ruben gruben@bigpond.net...
Thu Apr 23 04:39:59 CDT 2009


Like this? This basically just what you said, so I'm not sure what your 
exact question is. Is it just the use of eval that you weren't clear on?

import numpy as np
import matplotlib.pyplot as plt

eqs = [
['24 + 18.75*x + 4.79616e-013*x**2 + 31.25*x**3', 7.800, 7.600],
['28 + 22.5*x + 5.68434e-013*x**2 + 0*x**3', 8.000, 7.800],
]

for i in eqs:
     xr = np.linspace(i[2], i[1], 10)
     x = xr - i[2]
     y = eval(i[0])
     plt.plot(xr,y)
plt.show()


Gary R.

Bevan Jenkins wrote:
> Hello,
> 
> I have a series of equations that describe a curve.  Each equation is only 
> valid for a range of x values.  For example:
> 
> Equation	                                         Upperlimit Lowerlimit 
> 24 + 18.75 * x + 4.79616e-013 * x ** 2 + 31.25 * x ** 3	   7.800      7.600
> 28 + 22.5 * x + 5.68434e-013 * x ** 2 + 0 * x ** 3	   8.000      7.800
> 
> There is a lower limit for eqn1, after that the upper limit of the previous 
> eqn is lower of the next.
> 
> From (X) scale linear, To (Y) scale linear
> y = A0 + A1(x) + A2(x)2 + A3(x)3
> where:    x= value – LL
> 
> LL = the lower limit of the applicable equation
> 
> I would like to generate a sequence of values (linspace(min(lowerlimit),max
> (upperlimit)), work out x (x=value-approriate lower limit) and then using the 
> appropriate equation generate the y values.
> Below is the answer I am looking for
> 
> Value	x	y
> 7.600	0	24.000
> 7.650	0.05	24.941
> 7.700	0.1	25.906
> 7.750	0.15	26.918
> 7.800	0.2	28.000
> 7.850	0.050	29.125
> 7.900	0.100	30.25
> 7.950	0.150	31.375
> 8.000	0.200	32.5
> 
> Thanks for any help, 
> 
> Bevan Jenkins



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