`plcont`: Contour plot
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#### `plcont`: Contour plot

`plcont (` | f,
| nx,
| ny,
| kx,
| lx,
| ky,
| ly,
| clevel,
| nlevel,
| pltr,
| pltr_data`)`;

Draws a contour plot of the data in ``f`[`nx`][`ny`]`, using the ``nlevel`` contour levels specified by ``clevel``. Only the region of the matrix from ``kx`` to ``lx`` and from ``ky`` to ``ly`` is plotted out where all these index ranges are interpreted as one-based for historical reasons. A transformation routine pointed to by ``pltr`` with a generic pointer ``pltr_data`` for additional data required by the transformation routine is used to map indices within the matrix to the world coordinates.

`f` (``PLFLT_MATRIX``, input)

  A matrix containing data to be contoured.

`nx, ny` (``PLINT``, input)

  The dimensions of the matrix ``f``.

`kx, lx` (``PLINT``, input)

  Range of `x` indices to consider where `0 ≤ kx-1 < lx-1 < nx`. Values of `kx` and `lx` are one-based rather than zero-based for historical backwards-compatibility reasons.

`ky, ly` (``PLINT``, input)

  Range of `y` indices to consider where `0 ≤ ky-1 < ly-1 < ny`. Values of `ky` and `ly` are one-based rather than zero-based for historical backwards-compatibility reasons.

`clevel` (``PLFLT_VECTOR``, input)

  A vector specifying the levels at which to draw contours.

`nlevel` (``PLINT``, input)

  Number of contour levels to draw.

`pltr` (``PLTRANSFORM_callback``, input)

  A callback function that defines the transformation between the zero-based indices of the matrix ``f`` and the world coordinates.

  For the C case, transformation functions are provided in the PLplot library: `pltr0` for the identity mapping, and `pltr1` and `pltr2` for arbitrary mappings respectively defined by vectors and matrices. In addition, C callback routines for the transformation can be supplied by the user such as the `mypltr` function in `examples/c/x09c.c` which provides a general linear transformation between index coordinates and world coordinates.

  For languages other than C you should consult Part III, “ Supported computer languages ” for the details concerning how `PLTRANSFORM_callback` arguments are interfaced. However, in general, a particular pattern of callback-associated arguments such as a `tr` vector with 6 elements; `xg` and `yg` vectors; or `xg` and `yg` matrices are respectively interfaced to a linear-transformation routine similar to the above `mypltr` function; `pltr1`; and `pltr2`. Furthermore, some of our more sophisticated bindings (see, e.g., Chapter 10, Fortran Language) support native language callbacks for handling index to world-coordinate transformations. Examples of these various approaches are given in `examples/<language>x09*`, `examples/<language>x16*`, `examples/<language>x20*`, `examples/<language>x21*`, and `examples/<language>x22*`, for all our supported languages.

`pltr_data` (``PLPointer``, input)

  Extra parameter to help pass information to `pltr0`, `pltr1`, `pltr2`, or whatever callback routine that is externally supplied.

Redacted form: `plcont(f, kx, lx, ky, ly, clevel, pltr, pltr_data)` where (see above discussion) the `pltr, pltr_data` callback arguments are sometimes replaced by a `tr` vector with 6 elements; `xg` and `yg` vectors; or `xg` and `yg` matrices.

This function is used in examples 9, 14, 16, and 22.

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