# getData

Get current values of tunable-surface coefficients

## Syntax

``Kco = getData(K)``
``KcoJ = getData(K,J)``

## Description

````Kco = getData(K)` extracts the current value of a tunable surface. `K` is a `tunableSurface` object that represents the parametric gain surface:$K\left(n\left(\sigma \right)\right)=\gamma \left[{K}_{0}+{K}_{1}{F}_{1}\left(n\left(\sigma \right)\right)+\dots +{K}_{M}{F}_{M}\left(n\left(\sigma \right)\right)\right],$where: σ is a vector of scheduling variables.n(σ) is a normalization function (see the `Normalization` property of `tunableSurface`). γ is a scaling factor (see the `Normalization` property of `tunableSurface`).F1,...,FM are basis functions.K0,...,KM are tunable coefficients.`getData` evaluates `K` at the current values of the coefficients K0,...,KM.```
````KcoJ = getData(K,J)` extracts the current value of the coefficient of the Jth basis function FJ. Use `J` = 0 to get the constant coefficient K0.```

## Input Arguments

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Gain surface, specified as a `tunableSurface` object,

Index of basis function, specified as a nonnegative integer. To extract the constant coefficient K0, use `J` = 0.

## Output Arguments

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Current coefficient values of the tunable surface, returned as an array.

If the tunable surface `K` is a scalar-valued gain, then the length of `K` is `(M+1)`, where `M` is the number of basis functions in the parameterization. For example, if `K` represents the tunable gain surface:

`$K\left(\alpha ,V\right)={K}_{0}+{K}_{1}\alpha +{K}_{2}V+{K}_{3}\alpha V,$`

then `Kco` is the 1-by-4 vector [K0,K1,K2,K3].

For array-valued gains, each coefficient expands to the I/O dimensions of the gain. These expanded coefficients are concatenated horizontally in `Kco`. (See `tunableSurface`.) For example, for a two-input, two-output gain surface, `Kco` has dimensions `[2,2(M+1)]`.

Coefficient of the Jth basis function in the tunable surface parameterization, returned as a scalar or an array.

If the tunable surface `K` is a scalar-valued gain, then `KcoJ` is a scalar. If `K` is an array-valued gain, then `KcoJ` is an array that matches the I/O dimensions of the gain.