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How to plot two piecewise functions on same graph?

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Amna Habib 2022-7-23

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评论： Walter Roberson 2022-7-27

Picture1.png

I need to plot the attached functions on same plot. Please help me to write the Matlab code.

Thanks in advance!

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Walter Roberson 2022-7-23

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range = [-2 2];
fplot([f, g] , range)

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can you please send me full code?

I have tried but it is not running.

x = linspace(0, 1 );

f = @(x) (x<0.5) .* (30.*x) + (x>=0.5).* (70.*x)-20;

g = @(x) (x<0.5).* 30.*(1-x) + (x>=0.5).* 50-(70.*x) ;

figure

plot(x, [f(x); g(x)], 'linewidth', 1.5 )

grid

axis([min(x) max(x) 0 50 ])

xlabel('x ')

ylabel('Function Value ')

legend('f(x)','g(x)', 'Location','best ')

Amna Habib 2022-7-23

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The above was some other function. Both are not running.

x = linspace(0, 1 );

f = @(x) (x<0.5) .* (7-3.* 'sqrt'(-2.* ('ln'(2.*x)))) + (x>=0.5).*(7+2.* 'sqrt'(-2.* ('ln'(2-2.*x))));

g = @(x) (x<0.5).* (7-5.* 'sqrt'(-1.* ('ln'(2-2.*x)))) + (x>=0.5).*(7+4.* 'sqrt'(-1.* ('ln'(2.*x))));

figure

plot(x, [f(x); g(x)], 'linewidth', 1.5 )

grid

axis([min(x) max(x) 0 1 ])

xlabel('x ')

ylabel('Function Value ')

legend('f(x)','g(x)', 'Location','best ')

Walter Roberson 2022-7-23

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Your question defines symbolic formulas, so you need to use the symbolic toolbox or you need to modify the question.

x = linspace(0, 1 ).';
f = @(x) (x<0.5) .* (30.*x) + (x>=0.5).* (70.*x)-20;
g = @(x) (x<0.5).* 30.*(1-x) + (x>=0.5).* 50-(70.*x) ;
figure
plot(x, [f(x), g(x)], 'linewidth', 1.5 )

Amna Habib 2022-7-23

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Thanks, dear Walter Roberson!

Amna Habib 2022-7-23

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Can you please search the error in this code?

x = linspace(0, 1 );

f = @(x) (x<0.5) .* (7-3.* 'sqrt'(-2.* ('ln'(2.*x)))) + (x>=0.5).*(7+2.* 'sqrt'(-2.* ('ln'(2-2.*x))));

g = @(x) (x<0.5).* (7-5.* 'sqrt'(-1.* ('ln'(2-2.*x)))) + (x>=0.5).*(7+4.* 'sqrt'(-1.* ('ln'(2.*x))));

figure

plot(x, [f(x); g(x)], 'linewidth', 1.5 )

Walter Roberson 2022-7-23

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'ln'(2-2.*x)

if that was valid syntax at all, then it would mean that you want to take the vector of characters ['l' 'n'] and index that vector at the indices calculated by 2-2.*x, getting back a vector of characters.

By the way, matlab uses log() not ln()

Sam Chak 2022-7-23

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@Amna Habib, From where you learned

'sqrt'()

and

'ln'()

Walter Roberson 2022-7-23

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In Maple you could in theory use code such as

`sqrt`(x)

Everything inside the back quotes becomes part of an atomic name that can be used as an identifier, and there are ways to code symbols and unicode characters. So you could, for example, create a function named `2π`

Commonly, Maple strips the back quotes out in presentation mode (2d output) and renders the symbols, but there are some cases such as copy and paste in 1d (code) mode where it leaves the back quotes unless the characters involved form a valid identifier.

Sam Chak 2022-7-23

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@Walter Roberson, thanks for the background information. 👍

Amna Habib 2022-7-24

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Thanks @Walter Roberson

Amna Habib 2022-7-26

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编辑：Walter Roberson 2022-7-26

在 MATLAB Online 中打开

Ran in:

i have corrected this code but I think there is still an error in function 'g'. can you please mention?

here is the code. the the file showing graphical result is attached.

x = linspace(0, 1 );

f = @(x) (x<0.5) .* (7-3.* sqrt(-2.* (log(2.*x)))) + (x>=0.5).*(7+2.* sqrt(-2.* (log(2-(2.*x)))));

g = @(x) (x<0.5).* (7-5.* sqrt(-1.* (log(2-(2.*x))))) + (x>=0.5).*(7+4.* sqrt(-1.* (log(2.*x))));

figure

plot(x, [f(x); g(x)], 'linewidth', 1.5 )

Warning: Imaginary parts of complex X and/or Y arguments ignored.

Amna Habib 2022-7-26

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编辑：Amna Habib 2022-7-26

在 MATLAB Online 中打开

Ran in:

x = linspace(0, 1 ).';

f = @(x) (x<0.5) .* (30.*x) + (x>=0.5).* (70.*x)-20 ;

g = @(x) (x<0.5).* 30.*(1-x) + (x>=0.5).* 50-(70.*x ) ;

figure

plot(x, [f(x), g(x)], 'linewidth', 1.5 )

Sorry I have another confusion in this plot too. I didn't found any error but the graph is not correct as compared to the manual plotting. Here is the code and tghe graph file is attached in .png

Thanks in advance!

Walter Roberson 2022-7-26

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Ran in:

You should recheck your definition of g, as it is everywhere complex. Consider for example x = 0, then 2-2*x is 2-0, log(2) is positive, -1.*log(2) is negative, sqrt(-log(2)) is complex.

x = linspace(0, 1 );

f = @(x) (x<0.5) .* (7-3.* sqrt(-2.* (log(2.*x)))) + (x>=0.5).*(7+2.* sqrt(-2.* (log(2-(2.*x)))));

g = @(x) (x<0.5).* (7-5.* sqrt(-1.* (log(2-(2.*x))))) + (x>=0.5).*(7+4.* sqrt(-1.* (log(2.*x))));

figure

plot(x, [f(x); g(x)], 'linewidth', 1.5 )

Warning: Imaginary parts of complex X and/or Y arguments ignored.

syms X real

F(X) = piecewise( (X<0.5), (7-3.* sqrt(-2.* (log(2.*X)))), (X>=0.5), (7+2.* sqrt(-2.* (log(2-(2.*X))))), 0)

F(X) =

G(X) = piecewise( (X<0.5), (7-5.* sqrt(-1.* (log(2-(2.*X))))), (X>=0.5), (7+4.* sqrt(-1.* (log(2.*X)))), 0)

G(X) =

limit(F, X, 0)

ans =

limit(F, X, 1)

ans =

∞

limit(G, X, 0)

ans =

limit(G, X, 1)

ans =

Walter Roberson 2022-7-26

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Ran in:

x = linspace(0, 1 ).';

f = @(x) (x<0.5) .* (30.*x) + (x>=0.5).* (70.*x)-20 ;

g = @(x) (x<0.5).* 30.*(1-x) + (x>=0.5).* 50-(70.*x ) ;

figure

plot(x, [f(x), g(x)], 'linewidth', 1.5 )

syms X real

F(X) = piecewise((X<0.5), (30.*X), (X>=0.5), (70.*X)-20, 0 )

F(X) =

G(X) = piecewise((X<0.5), 30.*(1-X), (X>=0.5), 50-(70.*X), 0)

G(X) =

fplot([F, G], [0 1])

Amna Habib 2022-7-27

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Ran in:

x = linspace(0, 1 ).';

f = @(x) (x<0.5) .* (30.*x) + (x>=0.5).* (70.*x)-20 ;

g = @(x) (x<0.5).* 30.*(1-x) + (x>=0.5).* 50-(70.*x ) ;

figure

plot(x, [f(x), g(x)], 'linewidth', 1.5 )

syms X real

F(X) = piecewise((X<0.5), (30.*X), (X>=0.5), (70.*X)-20, 0 )

F(X) =

G(X) = piecewise((X<0.5), 30.*(1-X), (X>=0.5), 50-(70.*X), 0)

G(X) =

fplot([F, G], [0 1])

Amna Habib 2022-7-27

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Thanks a lot @Walter Roberson. I appreciate your effort.

Walter Roberson 2022-7-27

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Look more closely at your functions

f = @(x) (x<0.5) .* (30.*x) + (x>=0.5).* (70.*x)-20 ;
g = @(x) (x<0.5).* 30.*(1-x) + (x>=0.5).* 50-(70.*x ) ;

Notice that the -20 in f not being multiplied by any condition. Notice that the -70.*x in g is not being multiplied by any condition.

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