22 lines
626 B
APL
22 lines
626 B
APL
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∇RK4[⎕]∇
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∇
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[0] Z←R(Y¯ RK4)Y;T;YN;TN;∆T;∆Y1;∆Y2;∆Y3;∆Y4
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[1] (T R ∆T)←R
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[2] LOOP:→(R≤TN←¯1↑T)/EXIT
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[3] ∆Y1←∆T×TN Y¯ YN←¯1↑Y
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[4] ∆Y2←∆T×(TN+∆T÷2)Y¯ YN+∆Y1÷2
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[5] ∆Y3←∆T×(TN+∆T÷2)Y¯ YN+∆Y2÷2
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[6] ∆Y4←∆T×(TN+∆T)Y¯ YN+∆Y3
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[7] Y←Y,YN+(∆Y1+(2×∆Y2)+(2×∆Y3)+∆Y4)÷6
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[8] T←T,TN+∆T
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[9] →LOOP
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[10] EXIT:Z←T,[⎕IO+.5]Y
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∇
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∇PRINT[⎕]∇
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∇
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[0] PRINT;TABLE
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[1] TABLE←0 10 .1({⍺×⍵*.5}RK4)1
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[2] ⎕←'T' 'RK4 Y' 'ERROR'⍪TABLE,TABLE[;2]-{((4+⍵*2)*2)÷16}TABLE[;1]
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∇
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