Plotting a Piecewise function

I currently have this as a script:

function W
t= (1:56)
 while t>=1 & t<=28
     Ws
     t=48+3.6*t+.6363*t^2+.00963*t^3
 end
 while 28<t & t<=56
     Wr
     t=-1004+65.8*t
 end
  function Ws
      disp('t is greater than or equal to 1 and t is less than or equal to 28')
  end
  function Wr
      disp ('t is greater than 28 and less than or equal to 56')
  end
end
function graph;W (1,56)
N=1000;
n=(56-1)/N;
x=[1:.055:56];
i=1:length(x);
F(i)=W(x(i));
end
plot(x,F)
xlabel('Time')
ylabel('Body Weight')
end

Everything seems to go through matlab okay except that I cannot get it to graph. How can I change this to get it to graph?

[dpb]

Format the code so it's legible -- (put in line break and then two spaces before the first line of code...break lines as needed)

Answer 1

[Jan]

I think, this will not do what you want:

t = (1:56)
while t>=1 & t<=28
   Ws
   t=48+3.6*t+.6363*t^2+.00963*t^3
end

while produces the scalar dimensions of the condition by inserting an all():

while all(t>=1 & t<=28)

Now all elements of the vector t are transformed by the polynomial until any element is < 1 or > 28. Is this your intention?

Or do you want:

t = 1:56;
tt(1:28)  = 48+3.6*t+.6363*t^2+.00963*t^3;
tt(29:56) = -1004+65.8*t;

?

The next problem is:

function graph;W (1,56)

What should this do? The function W does not use input arguments. The function graph is not called from anywhere.

I recommend to read the Getting Started chapters of the documentation and to use the debugger to step through the code line by line until it gets clear, what's going on.

Answer 2

[Vivek Selvam]

This might be a starting place for a running code.

function graph
    N=1000;
    n=(56-1)/N;
    x=[1:n:56];
    for i=1:length(x)
        F(i)=W(x(i));
    end
    plot(x,F)
    xlabel('Time')
    ylabel('Body Weight')
end

function F = W(t)
    if t>=1 && t<=28
     Ws
     F=48+3.6*t+.6363*t^2+.00963*t^3
    end
    if 28<t && t<=56
     Wr
     F=-1004+65.8*t
    end
    function Ws
      disp('t is greater than or equal to 1 and t is less than or equal to 28')
    end
    function Wr
      disp ('t is greater than 28 and less than or equal to 56')
    end
end

Answer 3

[sixwwwwww]

Dear Lauren, do you need following functionality in your code:

j = 1:56;
t = zeros(1, length(j));
for i = 1:56
    if (i >= 1 && i < 29)
        disp('t is greater than or equal to 1 and t is less than or equal to 28')
        t(i) = 48 + 3.6 * i + .6363 * i^2 + .00963 * i^3;
    else if (i > 28 && i <= 56)
            disp ('t is greater than 28 and less than or equal to 56')
            t(i) = -1004 + 65.8 .* i;
        end
    end
end
N = 1000;
x = min(j):((max(j) - min(j)) / N):56;
F = interp1(j, t, x);
plot(x, F), xlabel('Time'), ylabel('Body Weight')

If yes then tell me which functions you need to do what work so that this code can be converted to functions