CODEWITHSUNDEEP
matlabfunctionhandle
mrgloom
mrgloom

Reputation: 21662

Handle to piece-wise function in Matlab

How to get handle to piece-wise functon in Matlab, for example

function f= AnaliticalF(t1,t2,t,curve)
  %solved in Maxima
  %solve([a3*t1^3+a2*t1^2+a1*t1+a0= L1, a3*t2^3+a2*t2^2+a1*t2+a0= L2, 3*a3*t1^2+2*a2*t1+a1= 0, 3*a3*t2^2+2*a2*t2+a1= 0],[a3,a2,a1,a0]);

  L1= curve(t1);
  L2= curve(t2);
  if (t <= t1)
    f= @(t)L1;
  elseif(t >= t2)
    f= @(t)L2;
  else
    a3=-(2*L1-2*L2)/(-t2^3+3*t1*t2^2-3*t1^2*t2+t1^3);
    a2=(-3*t2*L2-3*t1*L2+(3*t2+3*t1)*L1)/(-t2^3+3*t1*t2^2-3*t1^2*t2+t1^3);
    a1=-(6*t1*t2*L1-6*t1*t2*L2)/(-t2^3+3*t1*t2^2-3*t1^2*t2+t1^3);
    a0=(-3*t1^2*t2*L2+t1^3*L2+(3*t1*t2^2-t2^3)*L1)/(-t2^3+3*t1*t2^2-3*t1^2*t2+t1^3);

    f= @(t)a3*t^3 + a2*t^2 + a1*t + a0;
  end

end

then I want to apply function to array of elements:

f= AnaliticalF(t1,t2,t,curve);
y= arrayfun(f,trange);

but problem is that I need to specify t in AnaliticalF(t1,t2,t,curve) , but I want it t parameter free. So I need some 'smart' handle of function f such as call f(100) it can determine which part of piece-wise function to use without specifying parameter t.

Upvotes: 0

Views: 182

Answers (1)

Jens Boldsen
Jens Boldsen

Reputation: 1275

You can use indicator functions! For example if if you want the function f(t) = t when t < 0 and f(t) = t^2 when t >= 0, then you can define:

f = @(t) t*(t<0) + t^2*(t>=0);

This can of course easily be generalized to more advanced functions like the one of yours!

I hope this solves your problem.

EDIT: I decided to throw in the solution for your function:

function f= AnaliticalF(t1,t2,curve)
  L1= curve(t1);
  L2= curve(t2);
  a3=-(2*L1-2*L2)/(-t2^3+3*t1*t2^2-3*t1^2*t2+t1^3);
  a2=(-3*t2*L2-3*t1*L2+(3*t2+3*t1)*L1)/(-t2^3+3*t1*t2^2-3*t1^2*t2+t1^3);
  a1=-(6*t1*t2*L1-6*t1*t2*L2)/(-t2^3+3*t1*t2^2-3*t1^2*t2+t1^3);
  a0=(-3*t1^2*t2*L2+t1^3*L2+(3*t1*t2^2-t2^3)*L1)/(-t2^3+3*t1*t2^2-3*t1^2*t2+t1^3);
  f = @(t) (t <= t1)*L1 + (t >= t2)*L2 + ((t > t1)&(t<t2))*(a3*t^3 + a2*t^2 + a1*t + a0);
end

Upvotes: 1

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