Fix #522: float-guard the identity matrix test

Provide floating-point error margins in testing whether or not a matrix
is the identity matrix. This is done on a component by component basis.
Previously, the matrix values were compared directly to constants '0'
and '1', so the test could fail on account of floating-point errors.

HEN_HOUSE/egs++/egs_transformations.h

@@ -218,11 +218,20 @@ class EGS_EXPORT EGS_RotationMatrix {
  /*! \brief Returns \c true, if this object is approximately the unit matrix, \a false
  otherwise */
  bool isI() const {
- // compute square distance to unit matrix
- EGS_Float d2 = (rxx-1)*(rxx-1) + rxy*rxy + rxz*rxz +
- ryx*ryx + (ryy-1)*(ryy-1) + ryz*ryz +
- rzx*rzx + rzy*rzy + (rzz-1)*(rzz-1);
- return (d2 < epsilon*epsilon);
+
+ // compare with unit matrix components
+ if (fabs(rxy) < epsilon &&
+ fabs(rxz) < epsilon &&
+ fabs(ryx) < epsilon &&
+ fabs(ryz) < epsilon &&
+ fabs(rzx) < epsilon &&
+ fabs(rzy) < epsilon &&
+ fabs(rxx-1) < epsilon &&
+ fabs(ryy-1) < epsilon &&
+ fabs(rzz-1) < epsilon ) {
+ return true;
+ }
+ return false;
  };
 
  /*! \brief Returns the rotated a vector \f$ R \cdot \vec{v}\f$ */