What is the mathlab code for this figure?

[Divyajyoti Nayak]

Hi @Souhad, are you asking for code on how to make figures that look like the image or the logic for how to plot the curve shown in the figure? Either ways, it would be better if you could show what you have tried already.

Answer 1

[John D'Errico]

Why not try it? You might learn something.

Break the problem down into smaller problems, each of which you can solve yourself.

Start with plot. plot can plot a line or a curve, drawn thrugh a set of points. Or you can use fplot, if the curve is defined by some given function.

Next, those horizontal and vertical lines can be drawn, again by plot. But if you want to see lines terminated by arrowheads, the function quiver can do that.

You can add specific text annotation to a figure using the function text. And text can handle subscripts too.

And any of these plotting tools will allow you to control the color of a line easily.

Your figure has labels on the axes. In MATLAB, these will be controlled by the use of graphics handles.

So why not make an effort?

Start by learning to plot a simple curve.

help fplot

 fplot - Plot expression or function
    This MATLAB function plots the curve defined by the function y = f(x)
    over the default interval [-5 5] for x.

    Syntax
      fplot(f)
      fplot(f,xinterval)

      fplot(funx,funy)
      fplot(funx,funy,tinterval)

      fplot(___,LineSpec)
      fplot(___,Name,Value)
      fplot(ax,___)
      fp = fplot(___)
      [x,y] = fplot(___)

    Input Arguments
      f - Function to plot
        function handle
      xinterval - Interval for x
        [–5 5] (default) | two-element vector of form [xmin xmax]
      funx - Parametric function for x coordinates
        function handle
      funy - Parametric function for y coordinates
        anonymous function | function handle
      tinterval - Interval for t
        [-5 5] (default) | two-element vector of form [tmin tmax]
      ax - Axes object
        axes object
      LineSpec - Line style, marker, and color
        string scalar | character vector

    Name-Value Arguments
      MeshDensity - Number of evaluation points
        23 (default) | number
      Color - Line color
        [0 0.4470 0.7410] (default) | RGB triplet | hexadecimal color code |
        "r" | "g" | "b" | ...
      LineStyle - Line style
        "-" (default) | "--" | ":" | "-." | "none"
      LineWidth - Line width
        0.5 (default) | positive value
      Marker - Marker symbol
        "none" (default) | "o" | "+" | "*" | "." | ...
      MarkerEdgeColor - Marker outline color
        "auto" (default) | RGB triplet | hexadecimal color code | "r" |
        "g" | "b" | ...
      MarkerFaceColor - Marker fill color
        "none" (default) | "auto" | RGB triplet | hexadecimal color code |
        "r" | "g" | "b" | ...
      MarkerSize - Marker size
        6 (default) | positive value

    Output Arguments
      fp - One or more FunctionLine or ParameterizedFunctionLine objects
        scalar | vector

    Examples
      openExample('graphics/PlotExpressionExample')
      openExample('graphics/PlotParametricCurveExample')
      openExample('graphics/SpecifyPlottingIntervalAndPlotPiecewiseFunctionsExample')
      openExample('graphics/SpecifyLinePropertiesAndDisplayMarkersExample')
      openExample('graphics/ModifyPlotAfterCreationExample')
      openExample('graphics/PlotMultipleLinesInSameAxesExample')
      openExample('graphics/AddTitleAndAxisLabelsAndFormatTicksExample')

    See also fcontour, fmesh, fplot3, fsurf, hold, title, fimplicit,
      FunctionLine Properties, ParameterizedFunctionLine Properties

    Introduced in MATLAB before R2006a
    Documentation for fplot
       doc fplot

    Other uses of fplot

       symbolic/fplot

Next, try adding one horizontal or vertical line.

help quiver

 quiver - Quiver or vector plot
    This MATLAB function plots arrows with directional components U and V at
    the Cartesian coordinates specified by X and Y.

    Syntax
      quiver(X,Y,U,V)
      quiver(U,V)
      quiver(___,scale)
      quiver(___,LineSpec)
      quiver(___,LineSpec,'filled')
      quiver(___,Name,Value)
      quiver(ax,___)

      q = quiver(___)

    Input Arguments
      X - x-coordinates of arrow tails
        scalar | vector | matrix
      Y - y-coordinates of arrow tails
        scalar | vector | matrix
      U - x-components
        scalar | vector | matrix
      V - y-components
        scalar | vector | matrix
      LineSpec - Line style, marker, and color
        character vector | string
      scale - Arrow scaling factor
        nonnegative number | 'off'
      ax - Target axes
        Axes object

    Name-Value Arguments
      LineWidth - Width of arrow lines
        0.5 (default) | positive value
      ShowArrowHead - Arrowhead display
        'on' (default) | on/off logical value
      AutoScale - Use automatic scale factor
        'on' (default) | on/off logical value
      AutoScaleFactor - Automatic scale factor
        0.9 (default) | scalar

    Examples
      openExample('matlab/CreateQuiverPlotWindExample')
      openExample('matlab/DisableAutomaticScalingExample')
      openExample('matlab/PlotGradientAndContoursExample')
      openExample('matlab/SpecifyArrowColorQuiverExample')
      openExample('matlab/SpecifyAxesForQuiverPlotExample')
      openExample('matlab/ModifyQuiverPlotAfterCreationExample')

    See also contour, quiver3, meshgrid, Quiver Properties

    Introduced in MATLAB before R2006a
    Documentation for quiver
       doc quiver

Eat a programming elephant one byte at a time. (Well, this is not really that large of a problem, but at first, it will seem that way.) The only way to learn is by making an effort though.

Answer 2

[Star Strider]

It would help to have the function for .

Lacking it, this still requires annotation objects, and that is not always straightforward.

x = linspace(0, 9.5).';
y = x;
g = @(x) 10*(1 - exp(-0.3*x));                                          % Arbitrary ‘g(x)’

p = [2.5; 5.6; 6.35];

Lvg = (x >= 2) & (x <= 8);                                              % Defines ‘g(x)’ Plot Range

yx = @(xv) interp1(x, y, xv);

figure
plot(x(Lvg), g(x(Lvg)))                                                 % Plot Curve Segment
hold on
plot(x, y, '-k')
plot(p(3), g(p(3)), '.k', MarkerSize=12)
plot(p(3), yx(p(3)), '.k', MarkerSize=12)
plot(p(2), g(p(2)), '.k', MarkerSize=12)
hold off
Ax = gca;
Ax.XTickLabel = [];                                                     % Turn Off Tick Labels
Ax.YTickLabel = [];                                                     % Turn Off Tick Labels

xapf = @(x,pos,xl) pos(3)*(x-min(xl))/diff(xl)+pos(1);                  % 'x' Annotation Position Function
yapf = @(y,pos,yl) pos(4)*(y-min(yl))/diff(yl)+pos(2);                  % 'y' Annotation Position Function
xl = xlim;                                                              % Required
yl = ylim;                                                              % Required
pos = gca().Position;                                                   % Required

annotation('textarrow', xapf([0 yx(g(p(3)))],pos,xl), yapf([g(p(3)) g(p(3))],pos,yl), String='$p_3=g(p_2)\ $', Interpreter='LaTeX')
annotation('textarrow', xapf([0 0]+p(3),pos,xl), yapf([0 g(p(3))],pos,yl), String='$p_2$', Interpreter='LaTeX')
annotation('textarrow', xapf([0 yx(g(p(2)))],pos,xl), yapf([g(p(2)) g(p(2))],pos,yl), String='$p_2=g(p_1)\ $', Interpreter='LaTeX')
annotation('textarrow', xapf([0 0]+p(2),pos,xl), yapf([0 g(p(2))],pos,yl), String='$p_1$', Interpreter='LaTeX')
text(p(3), g(p(3))*1.01, '$(p_2,p_3)$', Interpreter='LaTeX', Vert='bottom', Horiz='center')
text(x(end), y(end), '$y=x$', Interpreter='LaTeX', Horiz='center', Vert='bottom')

●

This is an iillustration of how to use them, along with my normalisation functions ‘xapf’ and ‘yapf’. (They require ‘xl’, ‘yl’ and ‘pos’ so copy all of those.) They take (x,y) coordinates and return normalised coordinates to use with the annotation functions.

I leave the rest to you.

.