What does contour do?

contour(X, Y, Z, levels) draws iso-lines of the matrix Z projected on the XY plane using MATLAB-compatible defaults. When X and Y are omitted, RunMat assumes 1:m and 1:n axes. The default number of levels matches MATLAB (10).

Behaviour highlights

• Z must be a real matrix (host tensor or gpuArray). Axis vectors must be monotonically spaced but need not be uniform.
• Level inputs may be a scalar (number of levels) or an explicit vector. Vectors must be strictly increasing, matching MATLAB's contract.
• When gpuArray inputs are provided and the shared renderer is active, the iso-lines are generated by a GPU marching-squares kernel without copying data back to the host.
• The CPU fallback mirrors MATLAB semantics and produces identical iso-lines when no GPU is available.

Options

• 'LevelList', vec / 'Levels', vec – provide an explicit, strictly increasing vector of Z values to contour. vec may be a numeric vector (host tensor or gpuArray). If a scalar is supplied the helper interprets it as the requested number of levels, matching MATLAB.
• 'LevelStep', step – positive finite scalar that determines the spacing between contour levels.
• 'LevelListMode', 'auto' | 'manual' – 'auto' resets the helper to evenly spaced defaults; 'manual' requires the same call to also pass 'LevelList' or 'LevelStep'.
• 'LineColor', spec – accepts MATLAB color strings ("r", "magenta", etc.), RGB triples, or the literals 'auto'/'flat' (use the colormap) and 'none' (suppress iso-line overlays when paired with contourf).

Examples

contour(peaks(50));
contour(x, y, z, 20);
contour(x, y, z, [0, 0.5, 1.0]);
contour(x, y, z, 'LevelStep', 0.25, 'LineColor', 'none');