1 (* ========================================================================= *)
2 (* Heron's formula for the area of a triangle. *)
3 (* ========================================================================= *)
5 needs "Multivariate/measure.ml";;
9 (* ------------------------------------------------------------------------- *)
10 (* Eliminate square roots from formula by the usual method. *)
11 (* ------------------------------------------------------------------------- *)
14 let sqrt_tm = `sqrt:real->real` in
15 let is_sqrt tm = is_comb tm & rator tm = sqrt_tm in
17 let stms = setify(find_terms is_sqrt w) in
18 let gvs = map (genvar o type_of) stms in
19 (MAP_EVERY (MP_TAC o C SPEC SQRT_POW_2 o rand) stms THEN
20 EVERY (map2 (fun s v -> SPEC_TAC(s,v)) stms gvs)) (asl,w);;
22 (* ------------------------------------------------------------------------- *)
24 (* ------------------------------------------------------------------------- *)
31 let s = (a + b + c) / &2 in
32 measure(convex hull {A,B,C}) = sqrt(s * (s - a) * (s - b) * (s - c))`,
33 REPEAT GEN_TAC THEN REWRITE_TAC[LET_DEF; LET_END_DEF] THEN
34 REWRITE_TAC[MEASURE_TRIANGLE] THEN
35 CONV_TAC SYM_CONV THEN MATCH_MP_TAC SQRT_UNIQUE THEN
36 SIMP_TAC[REAL_LE_DIV; REAL_ABS_POS; REAL_POS] THEN
37 REWRITE_TAC[REAL_POW_DIV; REAL_POW2_ABS] THEN
38 REWRITE_TAC[dist; vector_norm] THEN
39 REWRITE_TAC[dot; SUM_2; DIMINDEX_2] THEN
40 SIMP_TAC[VECTOR_SUB_COMPONENT; ARITH; DIMINDEX_2] THEN
41 SQRT_ELIM_TAC THEN SIMP_TAC[REAL_LE_SQUARE; REAL_LE_ADD] THEN