Variable start values from Dict

Specific Domains Optimization (Mathematical)
1

I want to initialize a variable that is indexed by sets of strings to a dictionary with keys that are tuples of those same sets

A = ["cat","dog"]
R = ["E" , "W"]
X0 = Dict(
    ("cat","E") => 1.1,
    ("cat","W") => 1.2,
    ("dog","E") => 1.3,
    ("dog","W") => 1.4
)

m1 = Model()

@variable(m1, X[A,R], start = X0)

Gives: ERROR: Unable to use Dict... as the start value of a variable because it is not convertable to type ::Float64.

If I convert to an array …

nA = length(A)
nR = length(R)
X00 = zeros(2,2)
for i in 1:nA
    for j in 1:nR
        X00[i,j] = X0[A[i],R[j]]
    end
end

@variable(m1, X[A,R], start = X00)
@variable(m1, X[A,R], start = X00[i,j] for i in 1:nA for j in 1:nR)

Gives: ERROR: Passing arrays as variable starts without indexing them is not supported.
And : ERROR: Unrecognized positional arguments…
respectively.

Any thoughts on the best way to do this?

2

Ok, I figured this out. You can use the Dict directly. Here’s what worked:

A = ["cat","dog"]
R = ["E" , "W"]
X0 = Dict(
       ("cat","E") => 1.1,
       ("cat","W") => 1.2,
       ("dog","E") => 1.3,
       ("dog","W") => 1.4
)

m1 = Model()

@variable(m1, X[i = A,j = R], start = X0[i,j])

Thank you for the interest.

1 Like
3

You beat me to replying :smile: Yes, using indices is the correct way to solve this problem.