# How to create a graph

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Hi,

Could somebody advise me on how you would produce a graph like this in matlab

Thank you

### Accepted Answer

per isakson
on 1 Oct 2012

Edited: per isakson
on 31 Oct 2012

My approach, which requires some work,

- put data in a 2D array, C
- plot with the function, image
- Image type: Indexed (colormap)
- Define a colormap, with a special slot, e.g. 1, for "missing data", white in your case. The length of the colormap = 64 is enough.
- Map C carefully to the colormap, e.g. C(ii,jj)=1 for "missing data"
- User defined tick-labels on the axes
- and more

--- in response to comments I try to expand a bit ---

Variables

- cmap is a colormap of size [64x3]. It associates the numbers [1,2,..., 64] to 64 different colors. (64 is an example.)
- D is your 2D data array
- C is an array of the same size as D. The values of C are integers in the interval, [1,64].

You create a suitable colormap, cmap, with the colormapeditor. You add some specific colors to signal special values of D, e.g. "missing data", outliers of various kinds etc.

You define a function, which takes D as input and returns C, e.g.

function C = D2C( D )

C = zeros( size(D) ); % zeros will cause error if not replaced

C( isnan(D) ) = 1; % nans will e displayed with color #1

C( D >= upper ) = 2; % values above upper gets color #2

C( D <= lower ) = 3; % values below lower gets color #3

etc.

any command is ok as long as the values of C are integers [1,64]

assert( not( any( C(:)==0 ) ), .... )

end

and to display the graph

colormap( cmap )

image( C )

.

--- in response to John's comment on 19 Oct 2012 at 16:45 ---

%%Create some data

N = 1000;

Speed = transpose( logspace( 0, 2, N ) );

Acc = randn( N, 1 ) .* ( exp( - sqrt( 10*Speed/N ) ) );

Efficiency = ( Acc .* Speed );

nAccBins = 20; % Set resolution of image

nSpeedBins = 30;

Speed_upper = 100;

Speed_lower = 0;

Acc_upper = 3;

Acc_lower = -3;

ix_Speed = ceil( nSpeedBins * ( Speed - Speed_lower ) ...

/ ( Speed_upper - Speed_lower ) );

ix_Acc = ceil( nAccBins * ( Acc - Acc_lower ) ...

/ ( Acc_upper - Acc_lower ) );

M = accumarray( { ix_Speed, ix_Acc }, Efficiency, [], @mean, nan );

imh = imagesc( transpose( M ) );

axh = ancestor ( imh, 'Axes' );

set( axh, 'YDir', 'normal' )

Next step would be to map M to a special colormap with something like

C = D2C( M );

and display with

colormap( cmap )

image( C )

.

Backlog:

- axis, ticks and ticklabels
- colorbar

### More Answers (1)

Image Analyst
on 1 Oct 2012

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