z = x + I * y
.fi
-where \fIx\ =\ creal(z)\fP and \fIy\ =\ cimag(z)\fP.
+where
+.IR "x\ =\ creal(z)"
+and
+.IR "y\ =\ cimag(z)" .
.LP
Or one may use polar coordinates and gets
.nf
z = r * cexp(I * a)
.fi
-where \fIr\ =\ cabs(z)\fP
-is the "radius", the "modulus", the absolute value of \fIz\fP, and
-\fIa\ =\ carg(z)\fP
-is the "phase angle", the argument of \fIz\fP.
+where
+.IR "r\ =\ cabs(z)"
+is the "radius", the "modulus", the absolute value of
+.IR z ,
+and
+.IR "a\ =\ carg(z)"
+is the "phase angle", the argument of
+.IR z .
.LP
One has:
.nf