tasks a-s

Task/Numerical-integration/Forth/numerical-integration.fth

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+fvariable step
+
+defer method ( fn F: x -- fn[x] )
+
+: left                    execute ;
+: right  step f@       f+ execute ;
+: mid    step f@ 2e f/ f+ execute ;
+: trap
+  dup fdup  left
+      fswap right f+  2e f/ ;
+: simpson
+  dup fdup  left
+  dup fover mid 4e f* f+
+      fswap right f+  6e f/ ;
+
+: set-step ( n F: a b -- n F: a )
+  fover f- dup 0 d>f f/ step f! ;
+
+: integrate ( xt n F: a b -- F: sigma )
+  set-step
+  0e
+  0 do
+    dup fover method f+
+    fswap step f@ f+ fswap
+  loop
+  drop fnip
+  step f@ f* ;
+ \ testing similar to the D example
+: test
+  ' is method  ' 4 -1e 2e integrate f. ;
+
+: fn1  fsincos f+ ;
+: fn2  fdup f* 4e f* 1e f+ 2e fswap f/ ;
+
+7 set-precision
+test left    fn2  \ 2.456897
+test right   fn2  \ 2.245132
+test mid     fn2  \ 2.496091
+test trap    fn2  \ 2.351014
+test simpson fn2  \ 2.447732