MATLAB: I am trying to write a program to solve a quadratic equation using loops and braces. see the images for the exact problem and the attempt

matlab loop structures

Here is the exact problem:

Here is my attempt:

The answers I get are: y1=5.750000e+000 and y2=-238. However, I'm not convinced by this because I should be getting more than 2 answers, shouldn't I…? i.e. for=-9:0.5:9 generates a 1×37 array. Many thanks if anyone can spot the problems!

Best Answer

t = -9:.5:9;
n = numel(t);
out = zeros(n,1);
for jj = 1:n
    if t(jj) < 0
        out(jj) =  3*t(jj)^2 + 5;
    else
        out(jj) = -3*t(jj)^2 + 5;
    end
end

t = (-9:.5:9)';
out = -3*sign(t).*t.^2 + 5;

Related Solutions

MATLAB: “for” loops and branching help

You were close. Here is one way to do what you are trying to do, keeping with the FOR loop and IF statement use.

cnt = 0;
t = -9:.5:9
for ii = t
cnt = cnt + 1;
    if ii<0
        y(cnt)=(3*ii.^2)+5;
    else if ii>=0
       y(cnt)=(-3*ii.^2)+5;
        end
    end
end
plot(y,t)

Here is another way, without the cnt variable.

t = -9:.5:9;
for ii = 1:length(t)
      if t(ii)<0
          y(ii)=(3*t(ii).^2)+5;
      else if t(ii)>=0
         y(ii)=(-3*t(ii).^2)+5;
          end
      end
  end
  plot(y,t)

Also, here is a more MATLABish way of doing this, for future reference:

t2 = -9:.5:9
idx = t2>=0;
y2(idx) =   (-3*t2(idx).^2)+5;
y2(~idx) = (3*t2(~idx).^2)+5;
plot(y2,t2)

MATLAB: Want to combine two plots

Try this:

t = linspace(0, 50);
y1 = 100.0 - 90.0*exp(-0.0465*t);
y2 = 203.6 - 11.3*t;
y2 = y2 .* (y2 >= 0);                                   % Set Negative ‘y2’ To Zero 
y = y1 + y2;
figure
plot(t, y)
grid
xlabel('t')
ylabel('y')

That should do what you want.

Best Answer

Related Solutions

MATLAB: “for” loops and branching help

MATLAB: Want to combine two plots

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