Some TVM fun

[Albert Chan]

Hi, dm319

Plus42 does not evaluate f(ε), or its derivatives. Instead, it use taylor series:

f(ε) ≈ f(0) + f'(0)*ε
f'(ε) ≈ f'(0) + f''(0)*ε

RHS is easy to evaluate accurately, LHS may not, due to massive cancellations.

core_commands9.cc

Code:

    if (1 + i * i == 1) {
        phloat a = (pv + fv) / n;
        phloat b = pv - fv;
        phloat fp = (a + b) / 2;
        phloat fpp = (n * n - 1) * a / 6;
        f = a + pmt + fp * i;
        fp += fpp * i;
        i += (eps = -f / fp);
    } else {
    ...