If f ( a n ) f ( b n ) ≥ 0 at any point in the iteration (caused either by a bad initial interval or rounding error in computations), then print "Secant method fails." and return None .

Why does secant method fail?

The secant method is a little slower than Newton's method and the Regula Falsi method is slightly slower than that. ... If we do not have a good starting point or interval, then the secant method, just like Newton's method, can fail altogether.

What is drawback of secant method?

Disadvantages of secant method

It may not converge. There is no guaranteed error bound for the computed iterates. It is likely to have difficulty if f′(α) = 0. This means the x-axis is tangent to the graph of y = f (x) at x = α.