update

Task/Euler-method/REXX/euler-method.rexx

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+/* REXX ***************************************************************
+* 24.05.2013 Walter Pachl  translated from PL/I
+**********************************************************************/
+  Numeric Digits 100
+  T0=100
+  Tr=20
+  k=0.07
+
+  h=2
+  x=t0
+  Call head
+  do t=0 to 100 by 2
+    Select
+      When t<=4 | t>=96 Then
+        call o x
+      When t=8 Then
+        Say '...'
+      Otherwise
+        Nop
+      End
+    x=x+h*f(x)
+    end
+
+  h=5
+  y=t0
+  Call head
+  do t=0 to 100 by 5
+    call o y
+    y=y+h*f(y)
+    end
+
+  h=10
+  z=t0
+  Call head
+  do t=0 to 100 by 10
+    call o z
+    z=z+h*f(z)
+    end
+  Exit
+
+f: procedure Expose k Tr
+  Parse Arg t
+  return -k*(T-Tr)
+
+head:
+  Say 'h='h
+  Say '  t    By formula       By Euler'
+  Return
+
+o:
+  Parse Arg v
+  Say right(t,3) format(Tr+(T0-Tr)/exp(k*t),5,10) format(v,5,10)
+  Return