Page 423 - Excel for Scientists and Engineers: Numerical Methods

400 EXCEL: NUMERICAL METHODS

NewtRaph
Returns the value of the independent variable contained in variable necessary to make
the formula contained in expression have the value zero.

Syntax
NewtRaph(expression, variable, initial-value)
Expression reference to a cell containing a formula F(x)
Variable cell reference corresponding to x, the variable to be changed
initiaCvalue optional argument specifying the initial estimate to be used in the
Newton-Raphson procedure

Re marks
The argument expression can be either a reference to a cell that contains a formula,
or a name. The formula must depend on variable.
The argument variable must be a reference to a cell.
The argument initiaCvalue can be either a number, a reference to a cell containing
a number, a reference to a cell containing a formula, or a name.
The workbook can be set to either RlC1- or Al-style.
Use the optional argument initiaCvalue for functions that have more than one root,
to control the value of the root that is returned. For example, a cubic equation can
have three real roots, i.e., three different x-values that make y = 0. The root that
NewtRaph returns will depend on the trial value that you begin with.

Limitations
None of the precedent cells of the argument expression may contain references to
the argument reference.
The function cannot handle implicit references; that is, a name or range reference
cannot be used for a range of values.

Example
=NewtRaph(B3,A3), where 63 contains the worksheet formula
=A3A2-0.000001*SQRT(A3)-0.0000000051 and A3, the independent variable, contains
the value 1.2E-04, returns 0.00012814, a root of the function.

See Also
Bairstow, GoalSeek