Wednesday, September 16, 2009

GAMS/Mosek error message

From a log file:

MOSEK Warning 700    : 8 zero elements are specified in sparse input data.
MOSEK Warning 700    : 8 zero elements are specified in sparse input data.
MOSEK Warning 700    : 8 zero elements are specified in sparse input data.
MOSEK Warning 700    : 8 zero elements are specified in sparse input data.
MOSEK Warning 700    : 8 zero elements are specified in sparse input data.
MOSEK Warning 700    : 8 zero elements are specified in sparse input data.
MOSEK Warning 700    : 8 zero elements are specified in sparse input data.
MOSEK Warning 700    : 8 zero elements are specified in sparse input data.
MOSEK Warning 700    : 8 zero elements are specified in sparse input data.
MOSEK Warning 700    : 8 zero elements are specified in sparse input data.

First: issuing this message one time is more than enough.

I suspect this is related to a very small value in the GAMS model, below some a[i,j] tolerance. As GAMS will not export zero coefficients, a strict reading of these messages would mean there is a bug somewhere. So lets hope these error messages are somewhat poorly formulated and indeed this a matter of small values being present in the model.

Formulating correct and succinct error messages is very important (but often underestimated by software developers, myself included). They provide feedback to user when it really matters: when something is wrong and the user is most likely confused.