'...&MATRIX_NAME=PAM30&...' will set
this to PAM30.
Note: Using input value other than the default also requires change
in the 'GAPCOSTS' parameter. The allowed
list of input values to 'GAPCOSTS' for supported
matrces is given in 6.13.2. Use parameter
'MATRIX_PARAM' in wwwblast, which combines
these two parameters together. Equivalent in standalone command BLAST
'-M'.