CERN Program Library Long Writeup W5013 - CERNLIB ...

CALL GFANG
(P,COSTH*,SINTH*,COSPH*,SINPH*,ROTATE*)
P(3)
COSTH
SINTH
COSPH
SINPH
ROTATE
(REAL) input direction;
(REAL) cosine of the polar angle;
(REAL) sine of the polar angle;
(REAL) cosine of the azimuthal angle;
(REAL) sine of the azimuthal angle;
(LOGICAL) rotation flag, the rotation matrix is the unit matrix if ROTATE=.FALSE., i.e. no
rotation is needed;
Find the sine and cosine of the polar and azimuthal angle of the direction defined by the vector P. IfP is
along the z axis, ROTATE=.FALSE..
CALL GVROT
(DCOSIN,PART*)
PART(3) (REAL) direction to be rotated, overwritten on output;
DCOSIN(3) (REAL) direction of the new z axis;
Given the direction PART in a system of reference O, it returns the same direction in the system of reference
where the z axis of O is along DCOSIN. This routine is very useful when the θ angle of a secondary particle
is sampled in a reference frame where the parent particle moves along the z axis. Then the direction of the
secondary product in the MRS is returned by GVROT if DCOSIN is the direction of the parent particle.
A call to GVROT is equivalent to the following code:
DIMENSION PART(3), DCOSIN(3)
LOGICAL ROTATE
.
.
.
CALL GFANG(DCOSIN,COSTH,SINTH,COSPH,SINPH,ROTATE)
IF(ROTATE) CALL GDROT(PART,COSTH,SINTH,COSPH,SINPH)
with the advantage that inside GVROT all calculations are performed in double precision.
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