Use Matlab to graph piece wise function

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')

Answer 1

[Honglei Chen]

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);