Use Matlab to graph piece wise function

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Holly Hudson
Holly Hudson 2012-2-14
I am a college student working on a calculus project. I need to graph a piecewise function using Matlab with horizontal axis 1 to 56 and vertical axis 0 to 3000.
W(t)=48+3.64t+0.6363t^2+0.00963t^3, 1≤t≤28
-1004+65.8t, 28≤t≤56
My code so far for my function file is
function y = w(x)
if 1<=x && x<= 28
y = 48+3.64*x+0.6363*x^2+0.00963*x^3;
end
if x>28 && x<=56
y =-1004+65.8*x;
end
And my graph file so far is:
function graphw(xmin,xmax)
n=(xmax-xmin)/1000;
x=[xmin:n:xmax];
for i=1:length(x)
W(i)=w(x(i));
end
plot(x,w(x),'r.')
xlabel('x')
ylabel('y')

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回答（1 个）

Honglei Chen
Honglei Chen 2012-2-14
You need to use .^ when raising a vector to a power. This being said, I would just take advantage of the logical index:
x = 1:0.01:56;
y = zeros(size(x));
idx = find((x>=1) & (x<=28));
y(idx) = 48+3.64*x(idx)+0.6363*x(idx).^2+0.00963*x(idx).^3;
idx = find((x>28) & (x<=56));
y(idx) = -1004+65.8*x(idx);
plot(x,y);

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