import numpy as np
from gekko import GEKKO

# load data
x1 = np.array([1,2,5,3,2,5,2])
x2 = np.array([5,6,7,2,1,3,2])
ym = np.array([3,2,3,5,6,7,8])

# model
m = GEKKO()
c = m.Array(m.FV,3)
for ci in c:
    ci.STATUS=1
x1 = m.Param(value=x1)
x2 = m.Param(value=x2)
ymeas = m.Param(value=ym)
ypred = m.Var()
m.Equation(ypred == c[0] + c[1]*x1 + c[2]*x2)
# add constraint on sum(c[1]*x1) with vsum
v1 = m.Var(); m.Equation(v1==c[1]*x1)
con = m.Var(lb=0,ub=10); m.Equation(con==m.vsum(v1))
m.Minimize((ypred-ymeas)**2)
m.options.IMODE = 2
m.solve()
print('Final SSE Objective: ' + str(m.options.objfcnval))
print('Solution')
for i,ci in enumerate(c):
    print(i,ci.value[0])

# plot solution
import matplotlib.pyplot as plt
plt.figure(figsize=(8,4))
plt.plot(ymeas,ypred,'ro')
plt.plot([0,10],[0,10],'k-')
plt.xlabel('Meas')
plt.ylabel('Pred')
plt.savefig('results.png',dpi=300)
plt.show()