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# contourc

Low-level contour plot computation

## Syntax

C = contourc(Z)
C = contourc(Z,n)
C = contourc(Z,v)
C = contourc(x,y,Z)
C = contourc(x,y,Z,n)
C = contourc(x,y,Z,v)

## Description

contourc calculates the contour matrix C used by contour, contour3, and contourf. The values in Z determine the heights of the contour lines with respect to a plane. The contour calculations use a regularly spaced grid determined by the dimensions of Z.

C = contourc(Z) computes the contour matrix from data in matrix Z, where Z must be at least a 2-by-2 matrix. The contours are isolines in the units of Z. The number of contour lines and the corresponding values of the contour lines are chosen automatically.

C = contourc(Z,n) computes contours of matrix Z with n contour levels.

C = contourc(Z,v) computes contours of matrix Z with contour lines at the values specified in vector v. The length of v determines the number of contour levels. To compute a single contour of level i, use contourc(Z,[i i]).

C = contourc(x,y,Z), C = contourc(x,y,Z,n), and C = contourc(x,y,Z,v) compute contours of Z using vectors x and y to determine the x- and y-axis limits. x and y must be monotonically increasing.

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### Tips

C is a two-row matrix specifying all the contour lines. Each contour line defined in matrix C begins with a column that contains the value of the contour (specified by v and used by clabel), and the number of (x,y) vertices in the contour line. The remaining columns contain the data for the (x,y) pairs.

```C = [value1 xdata(1) xdata(2) ...
xdata(dim1) value2 xdata(1) xdata(2) ... xdata(dim2)...
dim1 ydata(1) ydata(2) ...
ydata(dim1) dim2 ydata(1) ydata(2) ...
ydata(dim2)];```

Specifying irregularly spaced x and y vectors is not the same as contouring irregularly spaced data. If x or y is irregularly spaced, contourc calculates contours using a regularly spaced contour grid, then transforms the data to x or y.