Shaun Shaun - 1 year ago 56
Python Question

where to place for loop in double sum to multiply an array

I have this following double sum, where my c-file (5x4 matrix) is multiplied with two arrays

. However, my end result isn't just one number but another array.

Now, I'm asking myself where I could include another for loop so that every entry within my two arrays are multiplied instead of the whole array.

g_T = [1,T,T**2,T*sy.log(T),T**2*sy.log(T)]
g_rho = [1,rho,rho**2,rho*sy.log(rho),rho**2*sy.log(rho)]

g_T_np = np.asarray(g_T)
g_rho_np = np.asarray(g_rho)

c = np.loadtxt("c_file2.txt")

for n in range(5):
for m in range(4):
free = c[n,m]*g_T_np*g_rho_np

f = open('Free_Energy_Values.txt', 'w')
print >> f, 'Free energy:', free

Thanks for your help.

EDIT: I'd like to calculate the Free Energy according to this formula.

Formula to calculate Free Energy
enter image description here

enter image description here

Answer Source

Notice, that the outer sum is from 1 to 4, and the inner sum is from 1 to 5. The simplest way to translate a formula into a programming language is to just put the same thing without optimizations.

The straight-forward way:

from math import log
import numpy as np

def F(T, rho):
    g_T = np.array([1, T, T ** 2, T * log(T), T ** 2 * log(T)])
    g_rho = np.array([1, rho, rho ** 2, rho * log(rho), rho ** 2 * log(rho)])
    c = np.loadtxt("c_file2.txt")
    total_sum = 0
    for i in range(4):
        for k in range(5):
            # we are traversing columns, not rows: notice [k,i], not [i,k]
            total_sum += c[k, i] * g_T[i] * g_rho[k]
    return total_sum

T = 1    # dummy value
rho = 2  # dummy value
print(F(T, rho))
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