# Documentation

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# streamtube

Create 3-D stream tube plot

## Syntax

`streamtube(X,Y,Z,U,V,W,startx,starty,startz)streamtube(U,V,W,startx,starty,startz)streamtube(vertices,X,Y,Z,divergence)streamtube(vertices,divergence)streamtube(vertices,width)streamtube(vertices)streamtube(...,[scale n])streamtube(axes_handle,...)h = streamtube(...z)`

## Description

`streamtube(X,Y,Z,U,V,W,startx,starty,startz)` draws stream tubes from vector volume data `U`, `V`, `W`.

The arrays `X`, `Y`, and `Z`, which define the coordinates for `U`, `V`, and `W`, must be monotonic, but do not need to be uniformly spaced. `X`, `Y`, and `Z` must have the same number of elements, as if produced by `meshgrid`.

`startx`, `starty`, and `startz` define the starting positions of the streamlines at the center of the tubes. The section Specifying Starting Points for Stream Plots provides more information on defining starting points.

The width of the tubes is proportional to the normalized divergence of the vector field.

`streamtube(U,V,W,startx,starty,startz)` assumes `X`, `Y`, and `Z` are determined by the expression

```[X,Y,Z] = meshgrid(1:n,1:m,1:p) ```

where `[m,n,p] = size(U)`.

`streamtube(vertices,X,Y,Z,divergence)` assumes precomputed streamline vertices and divergence. `vertices` is a cell array of streamline vertices (as produced by `stream3`). `X`, `Y`, `Z`, and `divergence` are 3-D arrays.

`streamtube(vertices,divergence)` assumes `X`, `Y`, and `Z` are determined by the expression

```[X,Y,Z] = meshgrid(1:n,1:m,1:p) ```

where `[m,n,p] = size(divergence)`.

`streamtube(vertices,width)` specifies the width of the tubes in the cell array of vectors, `width`. The size of each corresponding element of `vertices` and `width` must be equal. `width` can also be a scalar, specifying a single value for the width of all stream tubes.

`streamtube(vertices)` selects the width automatically.

`streamtube(...,[scale n])` scales the width of the tubes by `scale`. The default is `scale = 1`. When the stream tubes are created, using start points or divergence, specifying `scale = 0` suppresses automatic scaling. `n` is the number of points along the circumference of the tube. The default is `n = 20`.

`streamtube(axes_handle,...)` plots into the axes object with the handle `axes_handle` instead of into the current axes object (`gca`).

`h = streamtube(...z)` returns a vector of handles (one per start point) to `surface` objects used to draw the stream tubes.

## Examples

This example uses stream tubes to indicate the flow in the `wind` data set. Inputs include the coordinates, vector field components, and starting location for the stream tubes.

```figure load wind [sx, sy, sz] = meshgrid(80,20:10:50,0:5:15); streamtube(x,y,z,u,v,w,sx,sy,sz); % Define viewing and lighting view(3) axis tight shading interp; camlight; lighting gouraud ```

This example uses precalculated vertex data (`stream3`) and divergence (`divergence`).

```figure load wind [sx, sy, sz] = meshgrid(80,20:10:50,0:5:15); verts = stream3(x,y,z,u,v,w,sx,sy,sz); div = divergence(x,y,z,u,v,w); streamtube(verts,x,y,z,-div); % Define viewing and lighting view(3) axis tight shading interp camlight lighting gouraud ```