>> clear
>> format long
>> x=[0.3 0.4 0.5 0.6]

x =

   0.300000000000000   0.400000000000000   0.500000000000000   0.600000000000000

>> g=[-0.2488 -0.0493 0.1321 0.2988]

g =

  -0.2488000000000000  -0.0493000000000000   0.1321000000000000   0.2988000000000000

>> for k=1:4

l(k)=1

for i=1:4

if(i~=k)

l(k)=l(k)*(0-g(i))/(g(k)-g(i));

end

end

end

l =  1
l =

  -0.0467641470937923   1.0000000000000000

l =

  -0.0467641470937923   0.7795600606902545   1.0000000000000000

l =

  -0.0467641470937923   0.7795600606902545   0.3181954998337314   1.0000000000000000


>> p(1)=0+x(1)*l(1)

p = -0.0140292441281377
>> p(2)=p(1)+x(2)*l(2)

p =

  -0.0140292441281377   0.2977947801479641

>> p(3)=p(2)+x(3)*l(3)

p =

  -0.0140292441281377   0.2977947801479641   0.4568925300648298

>> p(3)=p(2)+x(3)*l(3)

p =

  -0.0140292441281377   0.2977947801479641   0.4568925300648298

>> p(4)=p(3)+x(4)*l(4)

p =

  -0.0140292441281377   0.2977947801479641   0.4568925300648298   0.4262976820067136


>> exp(p(4)*(-2))
ans =  0.426307072886187