OpenGL has no equivalent for MSINGLE, single-matrix mode. Though use of this mode has been discouraged, it is the default for IRIS GL. If your IRIS GL program uses the single-matrix mode, you need to rewrite it to use double-matrix mode only. OpenGL is always in double-matrix mode, and is initially in GL_MODELVIEW mode.
Most IRIS GL code in MSINGLE mode looks like this:
projectionmatrix();
where projectionmatrix is one of: ortho, ortho2, perspective, or window. To port to OpenGL, replace the MSINGLE-mode projectionmatrix function with:
glMatrixMode( GL_PROJECTION );
glLoadMatrix( identity matrix );
/* call one of these functions here: */
/* glFrustrum(), glOrtho(), glOrtho2(), gluPerspective()}; */
glMatrixMode( GL_MODELVIEW );
glLoadMatrix( identity matrix );