(11C) TVM for HP-11C

[Albert Chan]

(12-07-2020 06:55 PM)Albert Chan Wrote:  lua> i2 = 1.001*i1                    -- p1<0, i1 is a bit low

We can avoid thinking about direction, and how much adjustment, for i2

If zero interest, npmt = (pv+fv)/n + pmt, we can use this to get i2

lua> n, pv, pmt, fv = 36, 30000, -550, -15000
lua> i1 = guess_i(n, pv, pmt, fv)
lua> p1 = npmt(n, i1, pv, pmt, fv)

lua> function secant(x1,y1,x2,y2) return x1 - y1/(y2-y1)*(x2-x1) end
lua> i2 = secant(i1, p1, 0, (pv+fv)/n + pmt)
lua> p2 = npmt(n, i2, pv, pmt, fv)
lua> i3 = secant(i2, p2, i1, p1)

lua> table.foreachi({i1,i2,i3}, print)
1      0.005804795434882038
2      0.005805075946792827
3      0.005805072819418476