REDBLUE(M)是一个M x 3的矩阵，它定义了一种颜色映射关系。

REDBLUE(M), is an M-by-3 matrix that defines a colormap. 

颜色变化从亮蓝色开始，范围从蓝色到白色，然后从红色到亮红色。

The colors begin with bright blue, range through shades of blue to white, and then through shades of red to bright red. 

function c = redblue(m)

%REDBLUE    Shades of red and blue color map

%   REDBLUE(M), is an M-by-3 matrix that defines a colormap.

%   The colors begin with bright blue, range through shades of

%   blue to white, and then through shades of red to bright red.

%   REDBLUE, by itself, is the same length as the current figure's

%   colormap. If no figure exists, MATLAB creates one.

%

%   For example, to reset the colormap of the current figure:

%

%             colormap(redblue)

%

%   See also HSV, GRAY, HOT, BONE, COPPER, PINK, FLAG,

%   COLORMAP, RGBPLOT.

%   Adam Auton, 9th October 2009

if nargin < 1, m = size(get(gcf,'colormap'),1); end

if (mod(m,2) == 0)

   % From [0 0 1] to [1 1 1], then [1 1 1] to [1 0 0];

   m1 = m*0.5;

   r = (0:m1-1)'/max(m1-1,1);

   g = r;

   r = [r; ones(m1,1)];

   g = [g; flipud(g)];

   b = flipud(r);

else

   % From [0 0 1] to [1 1 1] to [1 0 0];

   m1 = floor(m*0.5);

   r = (0:m1-1)'/max(m1,1);

   g = r;

   r = [r; ones(m1+1,1)];

   g = [g; 1; flipud(g)];

   b = flipud(r);

end

c = [r g b];

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