The VALUE command evaluates the current value of all listed expressions, constants or variables, and prints the result in the form of \madxstatements on the assigned output file. \madbox VALUE, expression{, expression} ;

Example:
\madxmp a = clight/1000.;
value, a, pmass, exp(sqrt(2)); results in \madxmp a = 299792.458 ;
pmass = 0.938272046 ;
exp(sqrt(2)) = 4.113250379 ;