TVM solve for interest rate, revisited

[Albert Chan]

tvm program assumed END mode. Here is tvm wrapper for BEGIN mode.

Code:

function tvm_begin(n,i,pv,pmt,fv)
    if not fv  then return tvm(n,i,pv+pmt,pmt,fv)+pmt end
    if not pv  then return tvm(n,i,pv,pmt,fv-pmt)-pmt end
    if not pmt then return tvm(n,i,pv,pmt,fv) / (1+i) end
    return tvm(n,i,pv+pmt,pmt,fv-pmt)
end

> tvm_begin(n,i,360, .05/12, 100e3, nil, 0)
-534.5941473979808