How to write piecewise function in matlab for the following function. Please give me matlab code.

Question

soe min aung 2020-6-14

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https://ww2.mathworks.cn/matlabcentral/answers/547938-how-to-write-piecewise-function-in-matlab-for-the-following-function-please-give-me-matlab-code

评论： Star Strider 2020-6-14

clc
clear all
close all
syms x y
zeta0 = 0.5
L = 100;
W = 100;
h = 2;
g = 0.0098;
vt=sqrt(g*h)
c=1
v=c*vt
t1 = L/v
t = t1;
T1 = zeta0*v*t/(2*L)*(1-cos(pi/50*x)).*(1-cos(pi/100*(y+150))) ; 
T2 = zeta0*v*t/L*(1-cos(pi/50*x)) ;
T3 = zeta0*v*t/(2*L)*(1-cos(pi/50*x)).*(1-cos(pi/100*(y-150))) ; 
T = piecewise(0<=x<=100 , -150<=y<=-50, T1, 0<=x<=100 , -50<=y<=50, T2,0<=x<=100 , 50<=y<=150, T3)  
fplot(T)

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Answer 1

Star Strider 2020-6-14

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在 MATLAB Online 中打开

Creating an anonymous function for ‘T’ is much easier and faster than using piecwise and the Symbolic Math Toolbox for this:

zeta0 = 0.5
L = 100;
W = 100;
h = 2;
g = 0.0098;
vt=sqrt(g*h);
c=1;
v=c*vt;
t1 = L/v;
t = t1;
T1 = @(x,y) zeta0*v*t/(2*L)*(1-cos(pi/50*x)).*(1-cos(pi/100*(y+150))) ; 
T2 = @(x,y) zeta0*v*t/L*(1-cos(pi/50*x)) ;
T3 = @(x,y) zeta0*v*t/(2*L)*(1-cos(pi/50*x)).*(1-cos(pi/100*(y-150))) ; 
T = @(x,y) ((0<=x) & (x<=100) & (-150<=y) & (y<=-50)).*T1(x,y) + ((0<=x) & (x<=100) & (-50<=y) & (y<=50)).*T2(x,y) + ((0<=x) & (x<=100) & (50<=y) & (y<=150)).*T3(x,y);
[X,Y] = ndgrid(-100:5:200);
figure
surf(X,Y,T(X,Y))
grid on

See Anonymous Functions for details, if you are not familiar with them

.

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soe min aung 2020-6-14

Thank you all for your kindness. Specral thank.

Star Strider 2020-6-14

As always, my pleasure!

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Answer 2

Aditya Verma 2020-6-14

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https://ww2.mathworks.cn/matlabcentral/answers/547938-how-to-write-piecewise-function-in-matlab-for-the-following-function-please-give-me-matlab-code#answer_450996

编辑：Aditya Verma 2020-6-14

在 MATLAB Online 中打开

Hello there!

You can code a piecewise function using conditional statements. More specifically, using if-else clause in this case. An example of absolute value function would be:

function val = absVal(x)
    if x >= 0
        val = x;
    else
        val = -x;
    end
end

In a similar way, you can code your function.

If you are new to this concept, I recommend you to take the free MATLAB Onramp course, it will help you to get started with MATLAB.

UPDATE

If you have Symbolic Math Toolbox, you can use it to define this function in a similar way as you have mentioned. You can find similar examples here: https://www.mathworks.com/help/symbolic/piecewise.html#bu_gw85-1.