Newton root iteration calculator

Calculate final iterate and function value at final iterate with your own figures.

Your numbers

Use the units shown. Results update as you change valid inputs.

Use final iterate and function value at final iterate to compare changes to your inputs. The method and limits below explain the scope.

Examples

Examples

Try the starting example

Restricted expression f(x)
x - 2
Derivative expression, or auto
auto
Initial guess
0
Absolute residual tolerance
1e-10
Maximum iterations
20
Final iterate
2
Function value at final iterate
0
Newton updates used
1
Iteration status
Converged by residual
Trace: x, f(x)
0, -2; 2, 0

Try another scenario

Restricted expression f(x)
x^2 - 4
Derivative expression, or auto
auto
Initial guess
3
Absolute residual tolerance
1e-10
Maximum iterations
1
Final iterate
2.166667
Function value at final iterate
0.694444
Newton updates used
1
Iteration status
Iteration limit reached
Trace: x, f(x)
3, 5; 2.16666666667, 0.694444444444
Calculation method

Calculation method

Final iterate

Update x←x−f(x)/f′(x), using the supplied restricted derivative or a symbolic derivative of the validated expression.

Function value at final iterate

Evaluate f at the final iterate.

Newton updates used

Count completed updates; the initial observation is not an update.

Iteration status

Convergence requires the absolute residual tolerance; report iteration limit, zero-derivative error or stagnation honestly.

Trace: x, f(x)

Show the initial and every subsequent x/f(x) pair.

Symbols and units
a
Restricted expression f(x)
b
Derivative expression, or auto
c
Initial guess
d
Absolute residual tolerance
e
Maximum iterations

Use the units shown. A list keeps the order in which you enter its values. The symbol ^ means “raised to the power of”.

Assumptions & limits

Assumptions & limits

  • Scalar Newton iteration with at most 100 updates. Convergence is not guaranteed, and a supplied derivative is your responsibility. Zero derivatives, undefined evaluations and stagnation are explicit failures. Restricted expressions allow x (and y for ODEs), pi, e, + - * / ^, and sin, cos, tan, sec, csc, cot, exp, log, sqrt, abs, sinh, cosh, tanh, sech, csch, coth. Trigonometric arguments are in radians. Double-precision results are approximate. Numeric tables use 12 significant digits and display components at roundoff scale (32 machine epsilons relative to their row or relevant calculation scale) as zero; scalar diagnostics retain full precision.
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Further reading

SciPy: Newton root iteration ↗

Background reading; this does not imply endorsement or independent review of SumFizz.

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