Your formula nodes still have outputs as independent variables in the formulas. The upper formula node has no assignment statement. Thus, it has no output. The lower formula node assigns a value to a but not to c.
Both of the Zero finders return error -23021: Both function values have the same sign. If you calculate the values of the formula at 0 and 1, both are negative. Plotting the formula over that input range shows a rising zero crossing near 0.16 and a falling zero crossing near 0.56. The zero finders appear to work well only when a single zero crossing occurs between the values of start and end.
Lynn
