4.m

function output = sigmoid(incoming)
  output = 1/(1+(exp(incoming * -1)))
endfunction

%question 4
Wxh=-.1
Whh=.5
Why=.25
hbias=.4
ybias=0

x0 = 18
x1 = 9
x2 = -8

h0 = .2
h1 = .4
h2 = .8

y0 = .05
y1 = .1
y2 = .2

t0 = .1
t1 = -.1
t2 = -.2


z2 = Wxh * x2 + Whh * h1 + hbias
z1 = Wxh * x1 + Whh * h0 + hbias


% E1 = 1/2 (t1 -y1)^2
e1y1 = -(t1 - y1)

% y1 = Why * h1 + ybias
y1h1 = Why

%h1 = sigmoid(z1)
h1z1 = z1 * (1 - z1)


e1z1 = e1y1 * y1h1 * h1z1

% E2 = 1/2 (t2 -y2)^2
e2y2 = -(t2 - y2)

% y2 = Why * h2 + ybias
y2h2 = Why

%h2 = sigmoid(z2)
h2z2 = z2 * (1 - z2)

%z2 = Wxh * x2 + Whh * h1 + hbias
z2h1 = Whh



e2z1 = e2y2 * y2h2 * h2z2 + z2h1 * h1z1


Ez1 = e1z1 + e2z1



display("answr to question 4")

Ez1