Matlab - necesito ayuda con el algoritmo en octave o matlab de una funcion spline lineal

function U=splinecaballero(n,t,y,x)

if nargin==0

    n=10;

    t=rand(1,n);

    y=rand(1,n);

    x=rand/2

end

k=1;

for i=n-1:-1:1

    if x-t(i)>=0

        break;

    end

    U(k)=y(i)+(x-t(i))*(y(i+1)-y(i))/(t(i+1)-t(i));

    k=k+1;

end

>> U=splinecaballero

t =

    0.3464    0.8865    0.4547    0.4134    0.2177    0.1257    0.3089    0.7261    0.7829    0.6938

y =

    0.0098    0.8432    0.9223    0.7710    0.0427    0.3782    0.7043    0.7295    0.2243    0.2691

x =

    0.3365

U =

    0.4486    4.1969

>> n=10, t=rand(1,n), y=rand(1,n), x=rand, U=splinecaballero(n,t,y,x)

n =

    10

t =

    0.1386    0.5882    0.3662    0.8068    0.5038    0.4896    0.8770    0.3531    0.4494    0.9635

y =

    0.0423    0.9730    0.1892    0.6671    0.5864    0.6751    0.3610    0.6203    0.8112    0.0193

x =

    0.0839

U =

    1.3743    0.0866    0.7535    1.0040    3.2111    0.4746   -0.1170   -0.8071   -0.0710