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{alias:function}

h2. Name

*function* — manipulate data with mathematical expression

h2. Syntax
{panel:|borderStyle=solid|borderWidth=1|bgColor=#ffffaa}

*function* _function string_

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h2. Description

The *function* command can be used to manipulate data values in *Polydata* (i.e. points and lines) and *Structured Points* (i.e. grids). The specified function will be performed on each point in the dataset.

The *function string* can be a combination of several sub functions for each component you want to manipulate. Each sub function should be separated with a semi colon character (*;*) .

Each sub function is a combination of a target variable, an equal sign, and a mathematical expression.

for example:

{noformat:|borderWidth=1|bgColor=#eeeeee}
function "x = x + 100 ; y = x + y"
{noformat}
The variables in the function are always from the original dataset. In the example above, the x, and y variable in the second sub function will not be affected by result of the the first sub function.

The mathematical expression may contain these operators: \+, \-, \*, /, abs, exp, ceil, floor, ln, log10, sqrt, sin, sinh, cos, cosh, tan, tanh, asin, acos, atan, min, max, sign.

A conditional expression is also supported. An "if" test may be a part of the mathematical expression. The syntax should be if(condition, result if true, result if false).

For example:

{noformat:|borderWidth=1|bgColor=#eeeeee}
function "z = if(z<0, 5, z)"
{noformat}
will replace all values with z less than zero with 5.

h4.


h4. Polydata target variables:

x = the x value of the current point
y = the y value of the current point
z = the z value of the current point
s = the scalar value of the current point

h4. Structured Points target variables:

z = the value of the current point.
dx = point spacing in x direction.
dy = point spacing in y direction
origo_x = &nbsp;the X coordinate of the grid origo which is the lower left corner of the Structured Points dataset
origo_y = &nbsp;the Y coordinate of the grid origo which is the lower left corner of the&nbsp;Structured Points dataset

{color:#000000}{*}Common Function variables:*{color}


{color:#333333}The following variables are available to all datasets:{color}

x = the x value of the current point
y = the y value of the current point
z = the z value of the current point

h4. Polydata Function variables:

In addition to the common variables, the following variables are available for polydata

x\_ = the x value of the next point
y\_ = the y value of the next point
z\_ = the z value of the next point
\_x = the x value of the previous point
\_y = the y value of the previous point
\_z = the z value of the previous point
s\_ = the scalar value of the previous point
s = the scalar value of the current point
\_s = the scalar value of the next point

h4. Structured Points Function variables:

In addition to the common variables, the following variables are available for structured Points

xmin = the x value of the leftmost column of the&nbsp;Structured Points dataset
xmax = the x value of the rightmost column of the&nbsp;Structured Points dataset
ymin = the y value of the uppermost row of the&nbsp;Structured Points dataset
ymax = the y value of the bottommost row of the&nbsp;Structured Points dataset
dx = point spacing in x direction
dy = point spacing in y direction
rows = number of rows
cols = number of columns
origo_x = xmin = the x coordinate of the grid origo which is the lower left corner of the&nbsp;Structured Points dataset
origo_y = ymin = the Y coordinate of the grid origo which is the lower left corner of the&nbsp;Structured Points dataset

h2. Examples:

h4. Example 1: Switch Polydata x and y values&nbsp;


{noformat:|borderWidth=1|bgColor=#eeeeee}
function "x=y ; y=x"
{noformat}

h4. Example 2: Multiply z by 1000 (Structured Points or Poly Data)


{noformat:|borderWidth=1|bgColor=#eeeeee}
function "z=z*1000"
{noformat}

h4. Example 3: Translate polydata 100 in x direction


{noformat:|borderWidth=1|bgColor=#eeeeee}
function "x=x+100"
{noformat}

h4. Example 4: Translate structured points dataset100 in x direction


{noformat:|borderWidth=1|bgColor=#eeeeee}
function "origo_x=origo_x+100"
{noformat}

h4. Example 5: Use formula on a structured points dataset

This example may be run on a grid. It will replace the grid values with a wave pattern. Try the following command

{noformat:|borderWidth=1|bgColor=#eeeeee}
function "z=dy*sin(sqrt(x*x +y*y)/(dx*10))"
{noformat}

h2. See also

[swi - Switch coordinates] , [add - Add to dataset]

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