Pulling data from a for loop

I want to subtract Tskin at t = 10 from Tskin at t = 9. How do I do this?

T = 29; %  %C
Tambient = 20; % C
Tfilm = (T + Tambient)/2;
for t = 1:1:100
    k_air_2 = (2.4131 + 0.0078 * T) * 10^-2; % W/m*C
    rho_air = 1.2893 - 0.004 * Tfilm; % kg/m^3 
    mu_air = (0.0047 * Tfilm + 1.7164) * 10^-5; % kg/m*s
    k_air_ambient= (2.4131 + 0.0078 * Tfilm) * 10^-2; % W/m*C
    Re = Diameter_forearm * V * rho_air / mu_air; 
    
    h_air = (k_air_ambient/Diameter_forearm) .* (0.3 + ((0.62 * Re.^.5 * Pr.^.333)/((1 + (0.4 * Pr).^.667).^.25)).*(1 + ((Re/282000).^(5/8))).^.8) % J/s*K*m^2
 
    Uskin = (k_air_2/thickness_air) + (k_cotton/thickness_shirt) + (h_air) % J/s*K*m^2
    Uambient = (k_air_ambient/thickness_air) + (k_cotton/thickness_shirt) + (h_air)
    
    Tskin = [(T * Area * Cp_air * rho_air)/(t-(t-1)) + Qgen + (Uambient * Area * Tambient)]/((Area * Cp_air * rho_air / ((t-(t-1)))) + Uskin * Area);
    T = Tskin
    Tfilm = (T + Tambient)/2
    fprintf('Y is %.2f C after %d seconds ' ,Tskin,t)
end 

Answer 1

[Walter Roberson]

T = 29; %  %C
Tambient = 20; % C
Tfilm = (T + Tambient)/2;
Tskin = nan;
for t = 1:1:100
    k_air_2 = (2.4131 + 0.0078 * T) * 10^-2; % W/m*C
    rho_air = 1.2893 - 0.004 * Tfilm; % kg/m^3 
    mu_air = (0.0047 * Tfilm + 1.7164) * 10^-5; % kg/m*s
    k_air_ambient= (2.4131 + 0.0078 * Tfilm) * 10^-2; % W/m*C
    Re = Diameter_forearm * V * rho_air / mu_air; 
    
    h_air = (k_air_ambient/Diameter_forearm) .* (0.3 + ((0.62 * Re.^.5 * Pr.^.333)/((1 + (0.4 * Pr).^.667).^.25)).*(1 + ((Re/282000).^(5/8))).^.8) % J/s*K*m^2
 
    Uskin = (k_air_2/thickness_air) + (k_cotton/thickness_shirt) + (h_air) % J/s*K*m^2
    Uambient = (k_air_ambient/thickness_air) + (k_cotton/thickness_shirt) + (h_air)
    old_Tskin = Tskin;
    Tskin = [(T * Area * Cp_air * rho_air)/(t-(t-1)) + Qgen + (Uambient * Area * Tambient)]/((Area * Cp_air * rho_air / ((t-(t-1)))) + Uskin * Area);
    T = Tskin
    Tfilm = (T + Tambient)/2
    fprintf('Y is %.2f C after %d seconds ' ,Tskin,t)
    if t==10
        fprintf('Tskin(10) - Tskin(9) = %g\n', Tskin - old_Tskin);
    end
end 

[Justin Hayes]

Thank you very much, it works!