Subtracting the previous number in a for loop

Hello,

I can't seem to figure this one out and would appreciate some guidance.

I am attempting to create a for loop, as entering it manually for each point would be a pain in the rear, that would subtract values from itself.

i.e. say I have 100, I would like the for loop to subtract a found value from the previous value within the loop.

Here's the code.

close all
clear all
clc

%%Problem 1 

%Beam Data
 Avfy3 = 8.8;           %kips No. 3 Grade 40 double-leg 
 Av3 = Avfy3/(40);      %in2 for two
 Asfy4 = 190;           %kips No. 4 Grade 60
 As = Asfy4/(4*60);     %in2 for single bar
 As4 = Asfy4/(60);      %in2 for all bars
 bw = 12;               %in beam width
 jd = 20;               %in Comp to Long steel spacing

   S1 = 6;                %in, Spacing of No. 3 Bars
   S1n = 8;               %number of spaces
   S2 = 12;               %in, Spacing of No. 3 Bars
   S2n = 4;               %number of spaces

   P1 = 26.4;             %kips, End of L1 span
   P2 = P1;               %kips, End of L2 span
   PM = 52.8;             %kips, Middle of beam

   %Begin Solution
    disp('Part (a)')

    Length = [12,24,36,36,30,24....
        18,24,30,36,36,36,30,24,18,12,6];
    LAv = Length*Avfy3;
    Fjd = LAv/jd;

    Label = {'U12-L11','U12-L10','U12-L9','U11-L8','U10-L7','U9-L6','U8-L5'...
        'U8-L4','U8-L3','U8-L2','U7-L1','U6-L0','U5-L0','U4-LO'...
        'U3-LO','U2-LO','U1-LO'};

    for i = 1:17
      MemberForce = [Label(:,i),Fjd(:,i)];
    end

    %Sum moment @ U12
    M12 = PM*8-P1*4;      %kip-ft
    Mjd12 = (M12*12)/jd;  %kips
    M8 = PM*4;            %kip-ft
    Mjd8 = (M8*12)/jd;    %kips

    TF1 = Mjd12-Fjd(1,1)

    for i = 2:17
        TF = TF1 - Fjd(:,i)
    end

The problem area is the only for loop present. I don't know how to have Fjd subtracted from the previous value found and keep doing it until all the integers have been used up. TF1 is the initial point of interest. It just takes a new value of Fjd and subtracts it from TF1 instead of using say TF(1)-Fjd.

Any help would be great.

Thank you,

Cory M Powell

[Cory Powell]

Sorry the for loop with TF within it. The last for loop

Answer 1

[Walter Roberson]

    for i = 2:17
        TF1 = TF1 - Fjd(:,i)
    end

[Cory Powell]

Part (a) Cannot find an exact (case-sensitive) match for 'TF'

The closest match is: tf in C:\Program Files\MATLAB\R2015b\toolbox\control\control\@tf\tf.m

Error in Homework_9 (line 50) TF = TF - Fjd(:,i)

>> Thanks for the rapid answer, do you have any thoughts on this error message?

[Cory Powell]

Sorry you are right. I entered it incorrectly.

Thanks man, Cory