MATLAB: Not getting the right output for the if statement? [piecewise function]

if statementpiecewise

(Ajay deleted this so I (MF) am restoring it).

    % code
  function y = FcnEval(x)
  if x < -2
      y= -1./ ((x.^2) + 1)
  elseif -2 <= x < -1
      y= sin(x)
  elseif -1 <= x < 1
      y= x.^2
  elseif 1 <= x < 2
      y=2
  else  x >= 2     
      y=1./(x+1)
  end

but when I run the test case: x1 = 3; x2 = -2:2;

y1 = FcnEval(x1)
y2 = FcnEval(x2)

I'm supposed to get y1 = 0.2500

y2= -0.9093 1.0000 0 2.0000 0.3333

what am i doing wrong?

Best Answer

First off, I doubt your code runs since else if is not valid syntax. Second, I am pretty sure that 1 <= x < 2 is not doing what you think it is doing.

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MATLAB: Stuck on a simple cumsum prob

y = 0.5.*(x(3:end) - x(1:end-2));

Is linear interpolation between point 1 and 3, then between 2 and 4 and so on.

You cannot recover x from the linearly interpolated y unless you are given x(1) and x(end).

EDIT

Suppose you have 5 points only (for simplicity), then:

y2* = (x3-x1)/2;
y3* = (x4-x2)/2;
y4* = (x5-x3)/2;

I assume you know the series of y, i.e. are numbers, but x is unobserved, then you can see that the system has 5 unknowns (x1,...x5) in three equations. Thus, you can have a unique solution only if you are given x1 and x5.

Now, if you are given the x series for comparison reasons, you can guess x1 and x5 then retrieve the rest of the series and compare the distance between xNew and the original one. In an iterative fashion you can then tweak the guess and comapre again the two series, if the distance has dimished then continue tweaking the guess in the same direction until you reach distance = 0.

EDIT#2 You don't need exactly x1 and x5 but any two xi.

MATLAB: How to create a vector of this output

Try this:

[X,Y,Z] = ndgrid(-2:2);
Out = [Z(:),Y(:),X(:)]

producing:

Out =
    -2    -2    -2
    -2    -2    -1
    -2    -2     0
    -2    -2     1
    -2    -2     2
    -2    -1    -2
    -2    -1    -1
    -2    -1     0
    -2    -1     1
    -2    -1     2
    -2     0    -2
    -2     0    -1
    -2     0     0
    -2     0     1
    -2     0     2
         etc.

Best Answer

Related Solutions

MATLAB: Stuck on a simple cumsum prob

MATLAB: How to create a vector of this output

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