Doesn't Match legend color and plot color

legend color doesn't match the color of plot. I have already searched the other questions asked, but none of them seem to work for me.

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%% f(x) and its derivatives are declared as anonymous functions

f = @(x) 2.^x .* log(2).^0;

f_prime1 = @(x) 2.^x .* log(2).^1;

f_prime2 = @(x) 2.^x .* log(2).^2;

f_prime3 = @(x) 2.^x .* log(2).^3;

% Taylor series (polynomials) are declared as anonymous functions

% x0 : expansion point

% x : the point at which I would like to evaluate the Taylor series

%% 0th order Taylor series

T0 = @(x0,x) f(x0);

% 1st order Taylor series

T1 = @(x0,x) f(x0) + f_prime1(x0)*(x-x0);

% 2nd order Taylor series

T2 = @(x0,x) f(x0) + f_prime1(x0)*(x-x0) + f_prime2(x0)*(x-x0).^2/2;

% 3rd order Taylor series

T3 = @(x0,x) f(x0) + f_prime1(x0)*(x-x0) + f_prime2(x0)*(x-x0).^2/2 + f_prime3(x0)*(x-x0).^3/6;

%%

x0 = 1;

% Plot the Taylor series T0, T1, T2, T3 between -5 <= x <= +5 using expansion point x0 = 1;

x = linspace(-5,5,60);

y0 = T0(x0,x);

y1 = T1(x0,x);

y2 = T2(x0,x);

y3 = T3(x0,x);

yTrue = f(x);

%%

figure

plot(x,y0,'-ob','LineWidth',2)

hold on

plot(x,y1,'-ok','LineWidth',2)

hold on

plot(x,y2,'-or','LineWidth',2)

hold on

plot(x,y3,'-og','LineWidth',2)

hold on

plot(x,yTrue,'-oc','LineWidth',2)

xlabel('x')

ylabel('y')

legend('T0','T1','T2','T3','f(x) = 2^x')

set(gca, 'FontSize',18)

grid on

-------

Answer 1

[Star Strider]

There are several lines created for the first plot call. Return handles to each plot call and then choose the first line of each as the axis argument array to the legend call —

f = @(x) 2.^x .* log(2).^0;
f_prime1 = @(x) 2.^x .* log(2).^1;
f_prime2 = @(x) 2.^x .* log(2).^2;
f_prime3 = @(x) 2.^x .* log(2).^3;
% Taylor series (polynomials) are declared as anonymous functions
% x0 : expansion point
% x : the point at which I would like to evaluate the Taylor series
%% 0th order Taylor series
T0 = @(x0,x) f(x0);
% 1st order Taylor series
T1 = @(x0,x) f(x0) + f_prime1(x0)*(x-x0);
% 2nd order Taylor series
T2 = @(x0,x) f(x0) + f_prime1(x0)*(x-x0) + f_prime2(x0)*(x-x0).^2/2;
% 3rd order Taylor series
T3 = @(x0,x) f(x0) + f_prime1(x0)*(x-x0) + f_prime2(x0)*(x-x0).^2/2 + f_prime3(x0)*(x-x0).^3/6;
%%
x0 = 1;
% Plot the Taylor series T0, T1, T2, T3 between -5 <= x <= +5 using expansion point x0 = 1;
x = linspace(-5,5,60);
y0 = T0(x0,x);
y1 = T1(x0,x);
y2 = T2(x0,x);
y3 = T3(x0,x);
yTrue = f(x);
%%
figure
hp{1} = plot(x,y0,'-ob','LineWidth',2);
hold on
hp{2} = plot(x,y1,'-ok','LineWidth',2);
hold on
hp{3} = plot(x,y2,'-or','LineWidth',2);
hold on
hp{4} = plot(x,y3,'-og','LineWidth',2);
hold on
hp{5} = plot(x,yTrue,'-oc','LineWidth',2);
xlabel('x')
ylabel('y')
legend([hp{1}(1);hp{2}(1);hp{3}(1);hp{4}(1);hp{5}(1)], 'T0','T1','T2','T3','f(x) = 2^x')
set(gca, 'FontSize',18)
grid on

EDIT — Clarified explanation.

.

[kerem yaman]

thank you for your answer

[Star Strider]

My pleasure!

Answer 2

[Voss]

Your first plot call plots y0 vs x. y0 is a scalar and x is 1-by-60. Plotting these variables creates 60 lines, so when you make your legend, and it has 5 entries, legend uses the first 5 lines in the axes, all of which are from that first plot call.

Instead, plot with two 1-by-60 variables by repeating y0 60 times, for instance using y0*ones(1,60), which will create a single line.

%% f(x) and its derivatives are declared as anonymous functions
f = @(x) 2.^x .* log(2).^0;
f_prime1 = @(x) 2.^x .* log(2).^1;
f_prime2 = @(x) 2.^x .* log(2).^2;
f_prime3 = @(x) 2.^x .* log(2).^3;
% Taylor series (polynomials) are declared as anonymous functions
% x0 : expansion point
% x : the point at which I would like to evaluate the Taylor series
%% 0th order Taylor series
T0 = @(x0,x) f(x0);
% 1st order Taylor series
T1 = @(x0,x) f(x0) + f_prime1(x0)*(x-x0);
% 2nd order Taylor series
T2 = @(x0,x) f(x0) + f_prime1(x0)*(x-x0) + f_prime2(x0)*(x-x0).^2/2;
% 3rd order Taylor series
T3 = @(x0,x) f(x0) + f_prime1(x0)*(x-x0) + f_prime2(x0)*(x-x0).^2/2 + f_prime3(x0)*(x-x0).^3/6;
%%
x0 = 1;
% Plot the Taylor series T0, T1, T2, T3 between -5 <= x <= +5 using expansion point x0 = 1;
x = linspace(-5,5,60);
y0 = T0(x0,x);
y1 = T1(x0,x);
y2 = T2(x0,x);
y3 = T3(x0,x);
yTrue = f(x);
%%
figure
whos x y*

  Name       Size            Bytes  Class     Attributes

  x          1x60              480  double              
  y0         1x1                 8  double              
  y1         1x60              480  double              
  y2         1x60              480  double              
  y3         1x60              480  double              
  yTrue      1x60              480  double              

plot(x,y0*ones(1,60),'-ob','LineWidth',2)
hold on
plot(x,y1,'-ok','LineWidth',2)
hold on
plot(x,y2,'-or','LineWidth',2)
hold on
plot(x,y3,'-og','LineWidth',2)
hold on
plot(x,yTrue,'-oc','LineWidth',2)
xlabel('x')
ylabel('y')
legend('T0','T1','T2','T3','f(x) = 2^x')
set(gca, 'FontSize',18)
grid on

[kerem yaman]

It is work, thank you for your answer.

[Voss]

You're welcome!

Answer 3

[Emrah Can Ucar]

clear

clc

%% f(x) and its derivatives are declared as anonymous functions

f = @(x) 2.^x .* log(2).^0;

f_prime1 = @(x) 2.^x .* log(2).^1;

f_prime2 = @(x) 2.^x .* log(2).^2;

f_prime3 = @(x) 2.^x .* log(2).^3;

% Taylor series (polynomials) are declared as anonymous functions

% x0 : expansion point

% x : the point at which I would like to evaluate the Taylor series

%% 0th order Taylor series

T0 = @(x0,x) f(x0);

% 1st order Taylor series

T1 = @(x0,x) f(x0) + f_prime1(x0)*(x-x0);

% 2nd order Taylor series

T2 = @(x0,x) f(x0) + f_prime1(x0)*(x-x0) + f_prime2(x0)*(x-x0).^2/2;

% 3rd order Taylor series

T3 = @(x0,x) f(x0) + f_prime1(x0)*(x-x0) + f_prime2(x0)*(x-x0).^2/2 + f_prime3(x0)*(x-x0).^3/6;

%%

x0 = 1;

% Plot the Taylor series T0, T1, T2, T3 between -5 <= x <= +5 using expansion point x0 = 1;

x = linspace(-5,5,60);

y0 = T0(x0,x);

y1 = T1(x0,x);

y2 = T2(x0,x);

y3 = T3(x0,x);

yTrue = f(x);

%

hold on

grid on

xlabel('x')

ylabel('y')

set(gca, 'FontSize',18)

plot(x,y0,'LineWidth',2)

plot(x,y1,'LineWidth',2)

plot(x,y2,'LineWidth',2)

plot(x,y3,'LineWidth',2)

plot(x,yTrue,'LineWidth',2)

legend('T0','T1','T2','T3','f(x) = 2^x')

As far as I know, both marker and legend are not used in this way. But you can use it this way.

[kerem yaman]

thank you for your answer