|Syntax||RTP_R (imag, real)|
The function RTP_R takes a given rectangular co-ordinate and returns the so-called module (ie. the radius in polar co-ordinates). The result of RTP_R is always strictly positive and is not affected by the sign of the imag and real parameters, because of the symmetries of a circle.
Draw a rectangular pattern in green and the corresponding polar pattern again displayed as rectangular co-ordinates in white:
100 SCALE 10,-5,-5: PAPER 0: CLS 110 FOR x = -3 TO 3 STEP .4 120 FOR y = -3 TO 3 STEP 5E-2 130 INK 4: POINT x, y 140 INK 7: POINT RTP_R(x,y), RTP_T(x,y) 150 END FOR y 160 END FOR x
The same as the above example but the polar co-ordinates are treated even more unusually. If you correct the program and exchange a and b in line 140 then the two patterns will match exactly - this reveals what the RTP_… functions are actually doing:
100 SCALE 10,-5,-5: PAPER 0: CLS 110 FOR x = -3 TO 3 STEP .4 120 FOR y = -3 TO 3 STEP 2E-2 130 INK 4: POINT x, y 140 a = RTP_R(x,y): b = RTP_T(x,y) 145 INK 7: POINT b * COS(a), b * SIN(a) 150 END FOR y 160 END FOR x