TPEREL.TXT

LBL "TPEREL";search t=angle according r=Radius of isoperimeter curve of P  
            ;t is the angle to the vertical: between 0 and pi/4
            ;R is between P/4 and 0.900316316*P/4 (=SQRT(2*(2/PI)²)*P/4)
            ;Entry:
            ;  r ENTER P XEQ TPEREL
            ;Output:
            ;  t in X  (in radian)
            ;under CC BY SA creative commons 4.0 pascaldagornet at yahoo dot de
            ;R 20-21 (R 00-19 are used in PERELS/C and 3 and 4 and 6)
            ;date Oct13 2021 
            ;
            ;
RAD
STO 20      ;P in R20        
X<>Y          
STO 21      ;r stored for further use
X<>Y
4
/
X<Y?        
GOTO 01     ;check if a not larger than P/4 because that cannot be possible
2
PI
/
X^2
2
*
SQRT
RCL 21
X<Y?
GOTO 01
0,000000001  ;t start
PI
4
/
0,000000001
-           ; t end
"ZWFFT"
ASTO 06     ;if using SOL of MATH instead of SOLVE from Advantage
XEQ "SOLVE"   
RTN
LBL "ZWFFT"
STO 22
SIN
RCL 21
*
RCL 22
COS
RCL 21
*
;XEQ "PERELC" or XEQ "PERELS"
XEQ "PERELS"
RCL 20
-
RTN
LBL 01
"r TOO LARGE/SMALL"
AON
RTN
END