5 / VERSION 5A 4-26-77 (MH)
7 /X,THE ARGUMENT, IS REDUCED TO
11 /IF X>1.0 THEN ATAN(X)=PI/2 - ATAN(1/X)
12 /IF .5<X<1.0 THEN ATAN(X)=ATAN(1/2)+ATAN(2*X-(1/(X+2)))
13 /ATAN(X)=X FOR X<2^(-15)
118 /PICK UP RETURN AND ARGUMENT
139 /CHECK ARGAINST LOWER LIMIT
141 FSUB DATLOW /TOO SMALL?
142 JLE DATGO /YES ATAN(X)=X
147 /REDUCE X TO RANGE 0<X<.5
158 FLDA X /X=(2X-1)/(X+2)
166 FLDA ATN1S2 /C0=ATAN(1/2)
168 /COMPUTE ATAN USING ALGORITHM
190 FLDA LAMBDA /LAMBDA*X
192 FDIV DT1 /DIV BY THE REST
195 JXN DATD,1 /WAS X>1 ORIGINALLY?
196 FLDA PIS2 /Y ATAN(X)=PI/2-ATAN(X)
198 DATD, JXN DATRTN,0 /WAS X<0?