I am very new to matlab. Please state Why I am getting Subscripted assignment dimension mismatch error

clear

clc

close all

%% defination

m= 750; % mass of the system in kg

k= 50000; % Stiffness of system in N/m

c= 1000; % damping coefficient Ns/m

time= 0:0.01:1; %time in sec

x_0=0.01; % displacement intial condition

x_dot_0= 0; % velocity initial condition

y_0=0.01; % displacement intial condition

y_dot_0= 0; % velocity initial condition

syms x(t)

syms y(t)

D1x= diff(x,1);

D2x= diff(x,2);

D1y= diff(y,1);

D2y= diff(y,2);

%% computing

x= dsolve(m*D2x+k*x==0,x(0)==x_0, D1x(0)==x_dot_0,'t');

y= dsolve(m*D2y+k*y+c*D1y==0,y(0)==y_0, D1y(0)==y_dot_0,'t');

x_fun=matlabFunction(x) % to save solved function values

x_dot_fun = matlabFunction(diff(x))

y_fun=matlabFunction(y)

y_dot_fun = matlabFunction(diff(y))

x_t=x_fun(time);

y_t=y_fun(time);

u_t=x_dot_fun(time);

v_t=y_dot_fun(time);

difference=x_fun(t)-y_fun(t)

%% plotting

% plot parameters

clr=[236/255 237/255 237/255]; % standarad RGB code

unts='normalized'; % Screen resolution percentage

lnwidth=2; % line width of the plot

fnts=22; % font size in percent

pos_fig=[0.01 .1 0.98 0.8];

title_graph='Displacement and velocity vs time';

xlabel_graph='time' ;

ylabel_graph(1)='dispalcement';

ylabel_graph(2)='velocity';

%% plotting

fig= figure('colour',clr,'units',unts,'position',pos_fig);

[axes_graph, Line1,Line2] = plotyy(time,x_t,time,v_t);

Answer 1

[Bjorn Gustavsson]

In my version of matlab I have to assign strings using the string function

ylabel_graph(1) = string('dispalcement');
ylabel_graph(2) = string('velocity');

Maybe your version also supports double-quotes for string-generation:

ylabel_graph(1) = "dispalcement";
ylabel_graph(2) = "velocity";

I personally (straddling older matab-versions) would delay inserting variables of string-type a couple of years and stick with

cell-arrays of char-arrays to keep backwards compatibility:

ylabel_graph{1} = 'dispalcement';
ylabel_graph{2} = 'velocity';

HTH