Index in position 1 exceeds array bounds (must not exceed 1).

I am trying to run a code and it gives an error telling "Index in position 1 exceeds array bounds (must not exceed 1)."

I am trying to solve an equation which has 2 unkown variable, one of which i am assigning an array H=0:5 and trying to solve the other variable using the equation solver code. I have tried this with different equation and got the result however when i try to use the same concept for the equation in the below code it is showing the error. Any guidance or help would be highly appreciate.

the code is below where i am trying to get all values of "th" for every value of "z0".

clear; close all; clc;
g= 9.81;  %m/s^2
V1= 10; %m/s
V0= 6*V1; %m/s
tetha1= (pi/6)*(180/pi); %Porjectile inclination angle
x0= 10; %m
y0= 11; %m
hmax=10;
tp=0.1; %s
% The impact time th 
syms z0 th;
H=0:5;
t_h=zeros(101,7);
i=1;
for z0 = H
   Eq=(V1*th*sind(tetha1)+((1/2)*g*tp*(tp-2*th)))-(sqrt((4*(th-tp)^2*V1^2)-y0^2-(-x0+V1*th*cosd(tetha1))^2))==z0;
   P=solve(Eq,th,'IgnoreAnalyticConstraints',true);
   T=double(P);
   t_h(i,1)=z0;
   t_h(i,2)=T(2,1);
   i=i+1;   
end
fprintf('%2.5f\n',T);

Answer 1

[Ameer Hamza]

The statement

P=solve(Eq,th,'IgnoreAnalyticConstraints',true);

does not always return a solution. Sometimes it return an empty matrix. Therefore when you run these lines

T=double(P);
t_h(i,1)=z0;
t_h(i,2)=T(2,1);

On last line T(2,1) does not exist and MATLAB throws an error.

[mayank Shroff]

thanks for your response .

I have tried a code and its running in that. the code in which i have used similar style is as follows

clear; close all; clc;
% assignment 1 task [B]
% given data
clc; clear; close all;
g = 9.81; %m/s^2
V1 = 10; %m/s
V0 = 6*V1;
tetha1 = pi/6; %rad
x0 = 10; %m
y0 = 11; %m
%-----projectile hit target at time t_1----
t1 = 2*V1*sin(tetha1)/g;
fprintf('t_1 = %7.9f sec\n',t1)
%-----time lag to shoot bullet---------
tp = 0.1;
fprintf('t_p = %2.2f sec\n', tp)
%-----time to hit target--------
h_sol1 = zeros(101,7);
syms t H;
i=1;
for H = 0:0.05:5
 eqn = 2408.814* t^2 - 327.20*t + 8.06*t*H + 0.098*H - H^2 - 196 == 0 ;
 h_sol1(i,1) = H; %H
 sol1 = solve(eqn, t); %t time to hit the missile
 h_sol1(i,2) = sol1(2,1);
 i = i+1;
end
%fprintf('hit time = %5.5f sec', th)
f1 = figure;
figure(f1)
plot(h_sol1(:,1), h_sol1(:,2), 'LineWidth', 1, 'color', 'r')
xlabel('H(meter)')
ylabel('time to hit Projectile (sec)')
grid on;
title('H vs t')

[Ameer Hamza]

The equation in this code is quite simple

eqn = 2408.814* t^2 - 327.20*t + 8.06*t*H + 0.098*H - H^2 - 196 == 0 ;

It is just a quadratic equation which can be solved easily. However, your equation is more complicated, so solve() is not able to find a solution.

[mayank Shroff]

I have tried a different approach. I was able to get values till H=2 but when it goes to H=3 it shows error as below

%%----- Error------%%
Unable to perform assignment because the left and right sides have a different number of
elements.

Error in sym/privsubsasgn (line 1126)
                L_tilde2 =
                builtin('subsasgn',L_tilde,struct('type','()','subs',{varargin}),R_tilde);

Error in sym/subsasgn (line 963)
            C = privsubsasgn(L,R,inds{:});

Error in Part_b (line 14)
    p(i)=solve(E(i),t);
%%---- Error----%%

I was able to get the values for t from the equation till H=2; the code i used is as below

clear; close all; clc;
g = 9.81; %m/s^2
V1 = 10; %m/s
V0 = 6*V1;
tetha1 = 30; %rad
x0 = 10; %m
y0 = 11; %m
tp=0.1;
syms t H 
for H=[0;1;2;3]
    E=H+(sqrt((4*(t-tp)^2*V1^2)-y0^2-(-x0+V1*t*cosd(tetha1))^2))-((V1*t*sind(tetha1))+((1/2)*g*tp*(tp-2*t)));
end
for i=1:1:4
    p(i)=solve(E(i),t);
    s(i)=double(p(i));
end
plot(H,s(1,:),'Marker','x','Markersize',5,'color','r'); grid on; axis([0 2 0.6 max(s)+0.1]);

[Ameer Hamza]

This time again, for H=3, the solve() function returns an empty vector. MATLAB symbolic engine is not able to solve the equation for H=3, and it returns an empty vector. Since the symbolic engine is failing on your system of equations, I recommend using fsolve(), which is a numerical solver.