check_exoweights
checks whether the given exogenous transition weights for
simulation are correctly specified.
check_exoweights(M, exo_weights, how_many_rows, name_of_row_number)
Throws an error if the exogenous weights are incorrectly specified.
Exogenous transition weights weights given for simulation in some context.
how many rows the exogenous weights should have?
what is the name of the object whose value should determine the the number of rows in the exogenous weights?
Used by simulate.stvar, predict.stvar, GIRF, and GFEVD.