GurobiError: Unsupported type (<class 'str'>) for LinExpr addition argument

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Matin Amoozadeh Kozani

August 09, 2021 18:36

I have got this error, and I do not know what should I do.

# constants
numHub = len(C)
numCensustracts =len(df['D'])
#Set of hubs
H=np.arange(0,numHub)
# Set of census tracts
CT=np.arange(0,numCensustracts)

# first constraint
for j in CT:
m.addConstr(sum(x[i,j] for i in H)+ r[j]== df.D[j])

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2 comments

Official comment
Simranjit Kaur

Gurobi Staff

December 06, 2024 00:28
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Eli Towle

Gurobi Staff

August 09, 2021 18:50
Can you please post a full working code example that reproduces this issue? I.e., one that includes the definitions of \( \texttt{r} \), \( \texttt{df} \), \( \texttt{H} \), etc.

The error message states you are trying to add a \( \texttt{str} \) object to a linear expression object. I suspect that for some (or all) \( \texttt{j} \) in \( \texttt{CT} \), \( \texttt{r[j]} \) or \( \texttt{df.D[j]} \) is a \( \texttt{str} \) instead of a number. Here is an easy way to double-check the types of the elements in \( \texttt{r} \) and \( \texttt{df.D} \):
```
for j in CT:
    print(f'r[{j}] = {r[j]}, {type(r[j])}')
    print(f'df.D[{j}] = {df.D[j]}, {type(df.D[j])}')
```
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