contour
Contour plot of matrix
Syntax
Description
contour(
creates a contour plot containing
the isolines of matrix Z
)Z
, where Z
contains height
values on the xy plane. MATLAB^{®} automatically selects the contour lines to display. The column and row indices
of Z
are the x and y coordinates
in the plane, respectively.
contour(___,
specifies the
contour lines to display as the last argument in any of the previous syntaxes. Specify
levels
)levels
as a scalar value n
to display the contour
lines at n
automatically chosen levels (heights). To draw the contour
lines at specific heights, specify levels
as a vector of monotonically
increasing values. To draw the contours at one height (k
), specify
levels
as a twoelement row vector [k k]
.
contour(___,
specifies
additional options for the contour plot using one or more namevalue pair arguments. Specify
the options after all other input arguments. For a list of properties, see Contour Properties.Name,Value
)
contour(
displays the
contour plot in the target axes. Specify the axes as the first argument in any of the
previous syntaxes.ax
,___)
returns the
contour matrix M
= contour(___)M
, which contains the (x,
y) coordinates of the vertices at each level.
Examples
Contours of a Function
Create matrices X
and Y
, that define a grid in the xy plane. Define matrix Z
as the heights above that grid. Then plot the contours of Z
.
x = linspace(2*pi,2*pi); y = linspace(0,4*pi); [X,Y] = meshgrid(x,y); Z = sin(X)+cos(Y); contour(X,Y,Z)
Contours at Twenty Levels
Define Z
as a function of X
and Y
. In this case, call the peaks
function to create X
, Y
, and Z
. Then plot 20 contours of Z
.
[X,Y,Z] = peaks; contour(X,Y,Z,20)
Contours at One Level
Display the contours of the peaks
function at Z = 1
.
[X,Y,Z] = peaks; v = [1,1]; contour(X,Y,Z,v)
Dashed Contour Lines
Create a contour plot of the peaks
function, and specify the dashed line style.
[X,Y,Z] = peaks;
contour(X,Y,Z,'')
Contours with Labels
Define Z
as a function of two variables, X
and Y
. Then create a contour plot of that function, and display the labels by setting the ShowText
property to 'on'
.
x = 2:0.2:2; y = 2:0.2:3; [X,Y] = meshgrid(x,y); Z = X.*exp(X.^2Y.^2); contour(X,Y,Z,'ShowText','on')
Labels with Specific Number of Decimal Places and Units
Since R2022b
Create a contour plot that displays labels with one digit after the decimal point followed by the letter m
.
contour(peaks,[4 0 2],"ShowText",true,"LabelFormat","%0.1f m")
Labels in Different Units
Since R2022b
You can specify a function to format the labels when you need to calculate values. For example, you can define a function to calculate the label values in different units.
Define this function in a program file called mylabelfun.m
. The function converts the input from meters to feet and returns a string vector containing each value in meters with the equivalent value in feet in parentheses.
function labels = mylabelfun(vals) feetPerMeter = 3.28084; feet = round(vals.*feetPerMeter); labels = vals + " m (" + feet + " ft)"; labels(vals == 0) = "0 m"; end
Next, create a contour plot and specify the LabelFormat
property as a handle to mylabelfun
.
contour(peaks,[4 0 2],"ShowText",true,"LabelFormat",@mylabelfun)
Custom Line Width
Create a contour plot of the peaks
function. Make the contour lines thicker by setting the LineWidth
property to 3
.
Z = peaks; [M,c] = contour(Z); c.LineWidth = 3;
Contours Over Discontinuous Surface
Insert NaN
values wherever there are discontinuities on a surface. The contour
function does not draw contour lines in those regions.
Define matrix Z
as a sampling of the peaks
function. Replace all values in column 26
with NaN
values. Then plot the contours of the modified Z
matrix.
Z = peaks; Z(:,26) = NaN; contour(Z)
Input Arguments
X
— xcoordinates
matrix  vector
xcoordinates, specified as a matrix the same size as
Z
, or as a vector with length n
, where
[m,n] = size(Z)
. The default value of X
is the
vector (1:n)
.
When X
is a matrix, the values must be strictly increasing or
decreasing along one dimension and remain constant along the other dimension. The
dimension that varies must be the opposite of the dimension that varies in
Y
. You can use the meshgrid
function to create X
and
Y
matrices.
When X
is a vector, the values must be strictly increasing or
decreasing.
Example: X = 1:10
Example: X = [1 2 3; 1 2 3; 1 2 3]
Example: [X,Y] = meshgrid(1:10)
The XData
property of the Contour
object
stores the xcoordinates.
Data Types: single
 double
 int8
 int16
 int32
 int64
 uint8
 uint16
 uint32
 uint64
Y
— ycoordinates
matrix  vector
ycoordinates, specified as a matrix the same size as
Z
, or as a vector with length m
, where
[m,n] = size(Z)
. The default value of Y
is the
vector (1:m)
.
When Y
is a matrix, the values must be strictly increasing or
decreasing along one dimension and remain constant along the other dimension. The
dimension that varies must be the opposite of the dimension that varies in
X
. You can use the meshgrid
function to create the X
and
Y
matrices.
When Y
is a vector, the values must be strictly increasing or
decreasing.
Example: Y = 1:10
Example: Y = [1 1 1; 2 2 2; 3 3 3]
Example: [X,Y] = meshgrid(1:10)
The YData
property of the Contour
object
stores the ycoordinates.
Data Types: single
 double
 int8
 int16
 int32
 int64
 uint8
 uint16
 uint32
 uint64
Z
— zcoordinates
matrix
zcoordinates, specified as a matrix. This matrix must have at least two rows and two columns, and it must contain at least two different values.
Example: Z = peaks(20)
The ZData
property of the Contour
object
stores the zcoordinates.
Data Types: single
 double
 int8
 int16
 int32
 int64
 uint8
 uint16
 uint32
 uint64
levels
— Levels
scalar  vector
Contour levels, specified as a scalar whole number or a vector. Use this argument to
control the number and location of the contour lines. When you do not specify the
levels, the contour
function chooses the levels automatically.
To draw contour lines at n automatically chosen heights, specify levels as the scalar value n.
To draw the contour lines at specific heights, specify
levels
as a vector of monotonically increasing values.To draw contour lines at a single height
k
, specifylevels
as a twoelement row vector[k k]
.
Example: contour(peaks,10)
draws contour lines at 10 automatically
chosen heights on the peaks
function.
Example: contour(peaks,[4 0 4])
draws contour lines at 3 specific
heights on the peaks
function: 4
,
0
, and 4
.
Example: contour(peaks,[3 3])
draws contour lines to show where
the height of the peaks
function is
3
.
Data Types: single
 double
 int8
 int16
 int32
 int64
 uint8
 uint16
 uint32
 uint64
LineSpec
— Line style and color
character vector  string scalar
Line style and color, specified as a character vector or string scalar containing characters
and symbols. The characters and symbols can appear in any order. You can specify the
line style, line color, or both. Marker symbols such as 'o'
are
ignored.
Example: 'g'
is a green dashed line.
Line Style  Description  Resulting Line 

""  Solid line 

""  Dashed line 

":"  Dotted line 

"."  Dashdotted line 

Color Name  Short Name  Appearance 

'red'  'r' 

'green'  'g' 

'blue'  'b' 

'cyan'
 'c' 

'magenta'  'm' 

'yellow'  'y' 

'black'  'k' 

'white'  'w' 

ax
— Target axes
Axes
object
Target axes, specified as an Axes
object. If you do not specify
the axes, then contour
plots into the current axes.
NameValue Arguments
Specify optional pairs of arguments as
Name1=Value1,...,NameN=ValueN
, where Name
is
the argument name and Value
is the corresponding value.
Namevalue arguments must appear after other arguments, but the order of the
pairs does not matter.
Before R2021a, use commas to separate each name and value, and enclose
Name
in quotes.
Example: contour(Z,'ShowText','on')
displays the contour line
labels.
Note
The properties listed here are only a subset. For a complete list, see Contour Properties.
ShowText
— Contour line labels
'off'
(default)  on/off logical value
Contour line labels, specified as 'on'
or 'off'
,
or as numeric or logical 1
(true
) or
0
(false
). A value of 'on'
is equivalent to true
, and 'off'
is equivalent to
false
. Thus, you can use the value of this property as a logical
value. The value is stored as an on/off logical value of type matlab.lang.OnOffSwitchState
.
'on'
— Display the height values along the contour lines.'off'
— Do not label the contour lines.
LineWidth
— Line Width
0.5
(default)  positive value
Contour line width, specified as a positive value in points. One point equals 1/72 inch.
LabelSpacing
— Label spacing
144
(default)  scalar
Label spacing along the contour lines, specified as a scalar value in points, where one point is 1/72 inch. Use this property to control the number of contour labels along the contour lines. Smaller values produce more labels.
You must set the ShowText
property to 'on'
for
the LabelSpacing
property to have an effect.
If you use the clabel
function to display the labels,
then the LabelSpacing
property has no effect and the plot displays
one label per line.
Output Arguments
M
— Contour matrix
matrix
Contour matrix, returned as a tworow matrix of following form.
Z1, x_{1,1}, x_{1,2}, ..., x_{1,N1}, Z2, x_{2,1}, x_{2,2}, ..., x_{2,N2}, Z3, ... N1, y_{1,1}, y_{1,2}, ..., y_{1,N1}, N2, y_{2,1}, y_{2,2}, ..., y_{2,N2}, N3, ...
The columns of the matrix define the contour lines. Each contour line starts with a column containing Z and N values:
Zi — The height of the i^{th} contour line
Ni — The number of vertices in the i^{th} contour line
(x_{ij}, y_{ij}) — The coordinates of the vertices for the i^{th} contour line, where j ranges from 1 to Ni
c
— Contour object
Contour
object
Contour
object. Use this object to set properties after
displaying the contour plot.
Extended Capabilities
GPU Arrays
Accelerate code by running on a graphics processing unit (GPU) using Parallel Computing Toolbox™.
The contour
function
supports GPU array input with these usage notes and limitations:
This function accepts GPU arrays, but does not run on a GPU.
For more information, see Run MATLAB Functions on a GPU (Parallel Computing Toolbox).
Distributed Arrays
Partition large arrays across the combined memory of your cluster using Parallel Computing Toolbox™.
Usage notes and limitations:
This function operates on distributed arrays, but executes in the client MATLAB.
For more information, see Run MATLAB Functions with Distributed Arrays (Parallel Computing Toolbox).
Version History
Introduced before R2006a
See Also
Functions
Properties
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