1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
|
eliminate(eqns,vars):=block([teqns,sv,se,l,flag,dispflag],
modedeclare([l,i],fixnum,flag,boolean),flag:dispflag:false,
if not (listp(eqns) and listp(vars)) then error("the arguments must both be lists"),
if length(vars)>l:length(eqns) then error("more variables then equations"),
if l=1 then error("can't eliminate from only one equation"),
if length(vars)=l then (vars:reverse(vars),sv:vars[1], vars:reverse(rest(vars)),flag:true),
/* ?meqhk turns [a=b] into [a-b] */
eqns:map('?meqhk,eqns),
for v in vars do (
teqns:[],
for j:1 thru l while(freeof(v,first(eqns))) do(
teqns:cons(first(eqns),teqns), eqns:rest(eqns)),
if eqns=[] then eqns:teqns else (teqns:append(teqns,rest(eqns)), eqns:first(eqns), l:l-1, se:[],
for j:1 thru l do se:cons(resultant(eqns,teqns[j],v),se),
eqns:se)),
if flag then [rhs(apply('ev,[last(solve(eqns[1],sv)),eval]))] else eqns)$
|