# Curves

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This block can be used to define one or more …

They can be accessed from within <type>Curve</type> or <type>CurveScaled</type> parameters (more details on curves and curves scaled).

Following variables are accessible from CurveScaled:

• spatial: x, y, z
• temporal: t

## Example

Curves can be defined using the following block:

<curves>
<curve>
<name>CurveName</name>
<coords>
x_1 x_2 ... x_n
</coords>
<values>
y(x_1) y(x_2) ... y(x_n)
</values>
</curve>
</curves>

and can be called in “Properties” and “Parameters” inside “Expression”: CurveName(evaluation_value)

where evaluation_value is always exactly one value and refers to values provided inside <coords> </coords>. In the <expression>s using curves, time $t$ and global coordinate $x$, $y$, and $z$ can be used, and passed as curve’s argument for example:

<parameter>
<name>density</name>
<type>Function</type>
<expression>2000 - CurveName(x^2 + y^2) * TimeDependentCurve(t)</expression>
</parameter>

Curves can be useful to include information on variation of time dependent parameters. Those values can be called from the ’equation’ tag in ‘parameter’ if ’type’ ‘formula’ is selected.

## Interpolation

Curve represents a piece-wise linear function – the values between coordinates are interpolated linearly though. Outside of the curve’s range of definition the curve becomes a constant using the first value on the left and last value on the right.

This article was written by Feliks Kiszkurno. If you are missing something or you find an error please let us know.
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