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- ⍝ See Chaitin 1986, Physics in APL2, p. 14
- ⍝ Newton -- Orbits
- ⍝ Transcribed by Daniel Llorens - 2013
- ⍝ With GNU APL do apl -f newton.apl
- ∇NEWTON
- ⎕IO←0
- BODIES←2
- ORBIT←50 50⍴' '
- G←.6674E¯10
- T←0
- DELT←50
- M←6E24 10
- V←X←BODIES 3⍴0
- X[1;0]←1E7
- V[1;1]←6E3
- STEP←1
- LOOP:
- F←(⍳BODIES)∘.FORCE⍳BODIES
- A←⊃(+/F)÷M
- V←V+A×DELT
- X←X+V×DELT
- T←T+DELT
- DRAW
- →((12×15)≥STEP←STEP+1)/LOOP
- ∇
- ∇F←I FORCE J
- F←3⍴0
- →(I=J)/0
- DELX←X[J;]-X[I;]
- R←(+/DELX⋆2)⋆.5
- F←(G×M[I]×M[J]÷R⋆2)×(DELX÷R)
- ∇
- ∇DRAW
- ORBIT[25+⌊X[0;0]÷5E5;25+⌊X[0;1]÷5E5]←'E'
- ORBIT[25+⌊X[1;0]÷5E5;25+⌊X[1;1]÷5E5]←'⋆'
- →(0≠15|STEP)/0
- ' '
- 'TIME IN HOURS = ',⍕T÷60×60
- FRAME ORBIT
- ∇
- ∇FRAME PIC
- '|',('-',[0]PIC,[0]'-'),'|'
- ∇
- NEWTON
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