LinExpr Type Error float() argument must be a string or a number

[Saravana Murthy]

Hello,

I am a beginner to gurobipy. I have an objective function which is a sum of 3 LinExpr expressions. I have to maximize this function for "n" sets and I do this in a for loop.  I have a set of constraints as well.

The problem here is I get an error sometime (***NOT ALWAYS***) but exactly at the same line of code saying: File "linexpr.pxi", line 62, in gurobipy.LinExpr.__init__ (../../src/python/gurobipy.c:27663)

TypeError: float() argument must be a string or a number.

The code i have looks something like this.

for i in range(n):

     get inputs (code not shown here) - These are the number of variables

     model = Model("mymodel")

     x = model.addVars(5,vtype=GRB.BINARY,name= "x")

     y = model.addVars(5,vtype=GRB.BINARY,name= "y")

     z = model.addVars(6,vtype=GRB.BINARY,name= "z")

    coeff_x = [1 for j in range 5]

    coeff_y = [-1 for j in range 4]

    coeff_z = [1 for j in range 6]

    for each_i in range(len(y)):

           model.addConstr(z[i] == or_(x[i],y[i]))

Line 1    model.setObjective (LinExpr(coeff_x,x) +

Line 2                                     LinExpr(coeff_y,y) + 

Line 3                                   LinExpr(coeff_z,z)) 

    model.update()

    model.optimize()

When I run this, the error is always at line 3 telling 

"File "linexpr.pxi", line 62, in gurobipy.LinExpr.__init__ (../../src/python/gurobipy.c:27663)

TypeError: float() argument must be a string or a number "

This error does not happen always, quite random. For example if my n is set to 100, i get this error at i= 2 and sometimes at i = 65 etc. No real pattern. 

What can be the source of error.??

Thanks in advance

[Michael Winkler]

Hi Saravana,

>     for each_i in range(len(y)):
>            model.addConstr(z[i] == or_(x[i],y[i]))
>

above it should be model.addConstr(z[each_i] == or_(x[each_ii],y[each_i]))

Hopefully this fixes your problem.

Best,
Michael

[Saravana Murthy]

Hello Michael Winkler,

Thats just a typo. The error would be list index out of range. But still even if i fix that the problem persists

[Robert Luce]

Hello Saravana,

would it be possible to reduce your code to a minimal, executable python script that reproduces the behaviour you ar reporting?

Thanks,

Robert