How to plot two piecewise functions on same graph?

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

Thanks in advance!

Answer 1

[Walter Roberson]

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

[Amna Habib]

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]

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]

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]

Thanks, dear Walter Roberson!

[Amna Habib]

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]

'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]

@Amna Habib, From where you learned

'sqrt'()

and

'ln'()

[Walter Roberson]

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]

@Walter Roberson, thanks for the background information. 👍

[Amna Habib]

Thanks @Walter Roberson

[Amna Habib]

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]

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]

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]

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]

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]

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

[Walter Roberson]

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.