I am building some spring networks in order to build a model for rubber traction tests. I impose a displacement on some of my network's nodes, and I lock some others, then I run a minimization function on the system's energy in order to get the stabilized system.
First, wih the Nelder-Mead method, I had divergence issues, with system's energy growing with iteration number, so I am trying Powell's method. The direction vectors should help my function to 'move' my nodes in the correct direction.
Unfortunately, I still get an error.
Here is my code :
import scipy as sc
import scipy.optimize as opt
import numpy as np
### Scipy.optimize.minimize with Powell's method
# Algorithm' starting point
x0 = np.array([1., 1., 2., 1., 2., 3., 1., 2., 3., 1., 2., 3., 2., 3., 3., 0., 1.,
0., 2., 1., 0., 3., 2., 1., 4., 3., 2., 4., 3., 4.])
# Setting up the variables we will need
Bounds= opt.Bounds(lb=0, ub=10)
Direc = (np.array([[1, 1, 2, 1, 2, 3, 1, 2, 3, 1, 2, 3, 2, 3, 3, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 1, 2, 0, 1, 2,-1, 0, 1,-2,-1, 0,-2,-1,-2]]))
# Run the optimization function
x_pow = opt.minimize(minimize_energy, x0, method='Powell', tol=1e-6, bounds = Bounds,
options={'maxiter': 1e4, 'disp': True, 'direc':Direc})
And here is the error I get :
---------------------------------------------------------------------------
IndexError Traceback (most recent call last)
<ipython-input-23-f0bb1bfcaa17> in <module>
8 # Run the optimization function
9 x_pow = opt.minimize(minimize_energy, x0, method='Powell', tol=1e-6, bounds = Bounds,
---> 10 options={'maxiter': 1e4, 'disp': True, 'direc':Direc})
11
12 print('final x')
C:\Bib\envs\statmath3\lib\site-packages\scipy\optimize\_minimize.py in minimize(fun, x0, args, method, jac, hess, hessp, bounds, constraints, tol, callback, options)
598 return _minimize_neldermead(fun, x0, args, callback, **options)
599 elif meth == 'powell':
--> 600 return _minimize_powell(fun, x0, args, callback, **options)
601 elif meth == 'cg':
602 return _minimize_cg(fun, x0, args, jac, callback, **options)
C:\Bib\envs\statmath3\lib\site-packages\scipy\optimize\optimize.py in _minimize_powell(func, x0, args, callback, xtol, ftol, maxiter, maxfev, disp, direc, return_all, **unknown_options)
2638 delta = 0.0
2639 for i in ilist:
-> 2640 direc1 = direc[i]
2641 fx2 = fval
2642 fval, x, direc1 = _linesearch_powell(func, x, direc1,
IndexError: index 2 is out of bounds for axis 0 with size 2
I don't understand why I get an out of bounds while my direction vectors are the same length as x0, the parameter vector that will be optimized.
Thanks for your help!
