The PLplot Plotting Library: Programmer's Reference Manual
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### `plvect`: Vector plot

`plvect` (u, v, nx, ny, scale, pltr, pltr_data);

Draws a vector plot of the vector `(`u`[`nx`][`ny`],`v`[`nx`][`ny`])`. The scaling factor for the vectors is given by ``scale``. A transformation routine pointed to by ``pltr`` with a pointer ``pltr_data`` for additional data required by the transformation routine is used to map indices within the array to the world coordinates. The style of the vector arrow may be set using `plsvect`.

`u, v` (`PLFLT **`, input) Pointers to a pair of vectored two-dimensional arrays containing the x and y components of the vector data to be plotted. `nx, ny` (`PLINT`, input) Physical dimensions of the arrays ``u`` and ``v``. `scale` (`PLFLT`, input) Parameter to control the scaling factor of the vectors for plotting. If ``scale` = 0` then the scaling factor is automatically calculated for the data. If ``scale` < 0` then the scaling factor is automatically calculated for the data and then multiplied by `-`scale``. If ``scale` > 0` then the scaling factor is set to ``scale``. `pltr` (`void (*) (PLFLT, PLFLT, PLFLT *, PLFLT *, PLPointer)` , input) Pointer to function that defines transformation between indices in array ``z`` and the world coordinates (C only). Transformation functions are provided in the PLplot library: `pltr0` for identity mapping, and `pltr1` and `pltr2` for arbitrary mappings respectively defined by one- and two-dimensional arrays. In addition, user-supplied routines for the transformation can be used as well. Examples of all of these approaches are given in the Section called Contour Plots from C in Chapter 3. The transformation function should have the form given by any of `pltr0`, `pltr1`, or `pltr2`. `pltr_data` (`PLPointer`, input) Extra parameter to help pass information to `pltr0`, `pltr1`, `pltr2`, or whatever routine that is externally supplied.

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`plvasp`: Specify viewport using aspect ratio only | Up | `plvpas`: Specify viewport using coordinates and aspect ratio