# DimensionMismatch("arrays could not be broadcast to a common size; )

I’m trying to write a simple for loop!:
`for coef in reacions_to_test`
in which “reacions_to_test” is `2582-element Vector{Int64}`

but I face this error :

`DimensionMismatch("arrays could not be broadcast to a common size; got a dimension with lengths 2583 and 2")`

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I don’t think it’s possible to give meaningful help without an MWE that reproduces this. The error is relatively clear I think:

``````julia> rand(5) .* rand(7)
ERROR: DimensionMismatch("arrays could not be broadcast to a common size; got a dimension with lengths 5 and 7")
``````

but how you manage to get it is impossible to tell without an MWE and a stack trace that gives a line number.

If `reacions_to_test` is the source of the problem (there is a slightly discrepancy because it has length 2582 but the error message says 2583). Then you are trying to broadcast some operation over it and a two-element container, the other container should either have length 1 or the same size as `reacions_to_test`.