I need help with error in code.

I am working on a project and I can not get my program to run without error. I am new to matlab, so it may be something obvious that I am missing.

I was given a set of ODE's from Newton's laws of motion. I solved those ODE's and made them into A and B, seen below.

HERE IS THE WORK & FIGURE ---> PDF

This is the question I am trying to solve with the code below:

Consider a vehicle encountering a single bump that changes the road surface by 0.03m. The excitation can be modeled as a step input magnitude of 0.03 for Xse and using the numerical values in the table, select a suitable time range and time increment to compute the head displacement x1 in cm, and the head acceleration in g's for t=0 to tf, and the relative neck displacement x1-x2 for t=0 to tf.

Compute the system eigenvalues and show how to use them to help determind the final time (tf) and integration time increment so that three oscillations of the largest period can be seen and there are at least 30 time increments for the smallest period.

Plot head displacement vs time on one sheet, relative neck displacement vs time on a separate sheet, and head acceleration (g's) vs time.

I have emailed my professer for help multiple times, and I have not gotten a response for over a week. I just need to know if i am headed in the correct direction to be able to answer all of the given questions. I believe my code looks good so far, but i keep getting error messages.

m1=5.3;

m2=28.5;

m3=8.6;

m4=12.8;

c1=400;

c2=4750;

c3=4585;

c4=4475;

k1=310000;

k2=183000;

k3=162800;

k4=90000;

Input Xse=0.03*ustep(t)

DXse=0.03*d(t)

Let u=Us+UI

Then x=Xs+XI

A=[0 0 0 0 1 0 0 0; 0 0 0 0 0 1 0 0; 0 0 0 0 0 0 1 0; 0 0 0 0 0 0 0 1; -k1/m2 k1/m2 0 0 -c1/m2 c1/m2 0 0; k1/m2 -k1/m2 k2/m2 0 c1/m2 (-(c1/m2)-(c2/m2)) c2/m2 0; 0 k2/m3 (-(k2/m3)-(k3/m3)) k3/m3 0 c2/m3 (-(c2/m3)-(c3/m3)) c3/m3; 0 0 k3/m4 (-(k3/m3)-k4/m4) 0 0 c3/m4 (-(c3/m4)-(c4/m4))];

B=[0 0; 0 0; 0 0; 0 0; 0 0; 0 0; 0 0; c4/m4 k4/m4];

dX=A*x+B*Us

dX=A*x+B*UI

For Us

B=[0 0 0 0 0 0 0 k4/m4];

For UI

B=[0 0 0 0 0 0 0 c4/m4];

[Geoff Hayes]

Moved my answer to a comment

Anna - what error messages are you observing? Please copy and paste the full error message to this question. I see that there are some lines like

Let u=Us+UI

Then x=Xs+XI

Are these comments or pseudo-code? The "Let" and "Then" are invalid commands and so would cause errors (if either is the problem). Similarly, use of "Input" and "For" are incorrect.

[Geoff Hayes]

Moved Anna's comment to my answer to here

My revised code is shown below. I keep getting the error message:

"Error in Project41 (line 17) Input Xse=0.03*ustep(t)"

Am i using "input" incorrectly? If so, how do I change it so that it will run?

m1=5.3;
m2=28.5;
m3=8.6;
m4=12.8;
c1=400;
c2=4750;
c3=4585;
c4=4475;
k1=310000;
k2=183000;
k3=162800;
k4=90000;
Input Xse=0.03*ustep(t) 
DXse=0.03*d(t) 
Let u=Us+UI 
Then x=Xs+XI
A=[0 0 0 0 1 0 0 0; 0 0 0 0 0 1 0 0; 0 0 0 0 0 0 1 0; 0 0 0 0 0 0 0 1; -k1/m2 k1/m2 0 0 -c1/m2 c1/m2 0 0; k1/m2 -k1/m2 k2/m2 0 c1/m2 (-(c1/m2)-(c2/m2)) c2/m2 0; 0 k2/m3 (-(k2/m3)-(k3/m3)) k3/m3 0 c2/m3 (-(c2/m3)-(c3/m3)) c3/m3; 0 0 k3/m4 (-(k3/m3)-k4/m4) 0 0 c3/m4 (-(c3/m4)-(c4/m4))];
B=[0 0; 0 0; 0 0; 0 0; 0 0; 0 0; 0 0; c4/m4 k4/m4];
dX=A*x+B*Us
D=[0];
%for head displacement x1
Input Xse=0.03*ustep(t) 
DXse=0.03*d(t) 
Let u=Us+UI 
Then x=Xs+XI
dX=A*x+B*Us
Chead=[1 0 0 0 0 0 0 0] 
dt= 0.01;
tf=5;
t=0:dt:tf;
%For Us 
BS=[0 0 0 0 0 0 k4/m4 0]; 
sys=ss(A,BS,chead,D) 
[yS,t,x]= step(sys,t) ; 
%For UI 
BI=[0 0 0 0 0 0 0 c4/m4 ]; 
sys=ss(A,BS,Chead,D) 
[yI,t,x]= impulse(sys,t) ; 
Yhead=yS+yI 
Plot(t,Yhead) 
Input Xse=0.03*ustep(t) 
DXse=0.03*d(t) 
Let u=Us+UI 
Then x=Xs+XI
dX=A*x+B*Us
Ctorso=[ 0 1 0 0 0 0 0 0];
dt= 0.01;
tf=5;
t=0:dt:tf;
%For Us 
BS=[0 0 0 0 0 0 k4/m4 0]; 
sys=ss(A,BS,ctorso,D) 
[yS,t,x]= step(sys,t) ; 
%For UI 
BI=[0 0 0 0 0 0 0 c4/m4 ]; 
sys=ss(A,BS,Ctorso,D) 
[yI,t,x]= impulse(sys,t); 
Yhead=yS+yI 
plot(t,Ytorso-Yhead)
%Repeat for head acceleration x1double dot using Cheadacc=[-k1/m1 k1/m1 0 0 –c1/m1 c1/m1 0 0] and plot(t,x1doubledot/9.81) 
Input Xse=0.03*ustep(t) 
DXse=0.03*d(t) 
Let u=Us+UI 
Then x=Xs+XI
dX=A*x+B*Us
Cheadacc=[-k1/m1 k1/m1 0 0 -c1/m1 c1/m1 0 0];
dt= 0.01;
tf=5;
t=0:dt:tf;
%For Us 
BS=[0 0 0 0 0 0 k4/m4 0]; 
sys=ss(A,BS,Cheadacc,D) 
[yS,t,x]= step(sys,t); 
%For UI 
BI=[0 0 0 0 0 0 0 c4/m4 ]; 
sys=ss(A,BS,Cheadacc,D) 
[yI,t,x]= impulse(sys,t) ; 
Yhead=yS+yI 
plot(t,x1doubledot/9.81)

[Geoff Hayes]

Anna - how do you want to be using input? Are you asking the user to enter a value? What should be happening with

Input Xse=0.03*ustep(t) 
DXse=0.03*d(t) 
Let u=Us+UI 
Then x=Xs+XI

? What is ustep?