Error while plotting sym function

Hello,

I have prepared a code as follows:

%A check for initial tilt angle k
syms v
I = input("Body moment of inertia? in kgm^2"); % I = 150kgm^2
l = input("Length of body? in m "); % l= 0.5m
b = input("Breadth of body? in m "); % b= 0.13m
w = input("Height of body? in m "); % w= 0.5m
d = input("cross-section diameter of towed array? in m "); % d= 0.72m
h = input("length of towed array? in m "); % h= 4.713m
s = input("span of hydrofoil? in m "); % s= 0.53m
c = input("chord of hydrofoil? in m "); % c=0.15m
yf = input("y-coordinate of application of hydrofoil force? in m "); % yf= 0.2
xf = input("x-coordinate of application of hydrofoil force? in m "); % xf= 0.2
yc = input("y-coordinate of application of towed array force? in m "); % yc= 0.2
xc = input("x-coordinate of application of towed array force? in m "); % xc= 2.606
yt = input("y-coordinate of application of towing force? in m"); % yt= 0.25
xt = input("x-coordinate of application of towing force? in m"); % xt= 0
yb = input("y-coordinate of application of body force? in m"); % yb= 
xb = input("x-coordinate of application of body force? in m"); % xb= 0
xcm = input("center of gravity x-coordinate?"); % xcm= 1.3724m
ycm = input("center of gravity y-coordinate?"); % ycm= 0.0985m
xcb = input("center of buoyancy x-coordinate?"); % xcb= 1.3724m
ycb = input("center of buoyancy y-coordinate?"); % ycb= 0.0985m
lf = ycm+yf; 
bf = xcm-xf; 
lc = yc-ycm; 
bc = xc-xcm; 
lt = yt-ycm; 
bt = xcm; 
lb = ycm+yb;
bb = xcm;
lB = ycb-ycm;
bB = xcb-xcm;
beta = input("Hydrofoil angle of attack? in rad "); %beta= 0.17 radians, 10 degrees
AR = s/c; %Aspect ratia of hydrofoil
k = input("Initial tilt? in m/s "); %v= 10m/s
%Cdc = input("Drag coefficient cable? "); %Cdc= 0.82
%Clc = input("Lift coefficient cable? "); %Clc= 0
Cf = input("Skin friction coefficient"); %Ct=Cn=Cf=0.012
Cdp = input("profile drag coefficient"); %Cdp=0.82
Cdc = Cf*cosd(k); %Cdc= 0.82
Clc = Cf*sind(k)+Cdp*(sind(k)^2); %Clc= 0
Cd = input("Drag coefficient body? "); %Cd= 2.05
Cl = input("Lift coefficient body? "); %Cl= 0
Clf = 2*pi*(AR/(AR+3))*beta; %Lift coefficient of hydrofoil
Cdf = (Clf^2)/(pi*AR); %drag coefficient of hydrofoil
rhow = input("Fluid density? in kg/m^3 "); %rhow= 1000kg/m^3
rhos = input("Stabiliser density? in kg/m^3"); %rhow= 1483.68kg/m^3
rhoc = input("Towed array density? in kg/m^3 "); %rhoc= 1000kg/m^3
%v = input("Velocity? in m/s "); %v= 10m/s
pi = 3.14;

xk = xcm*cosd(k)+ycm*sind(k); %center of mass x-coordinate after some tilt k
yk = -xcm*sind(k)+ycm*cosd(k); %center of mass y-coordinate after some tilt k

Vb = l*b*w; %Body volume
Mb = rhos*Vb; %Body mass
Mwb = rhow*Vb; %Body displaced water mass

Vf = 2*5*s*0.12*c*(0.1979*(c^1.5)-0.063*(c^2)-0.1172*(c^3)+0.0711*(c^4)-0.0203*(c^5)); %Hydrofoil volume
Mf = rhos*Vf; %Hydrofoil mass
Mwf = rhow*Vf; %Hydrofoil displaced water mass

Vc = pi*((d/2)^(2))*h; %towed array volume
Mc = rhoc*Vc; %towed array mass
Mwc = rhow*Vc; %towed array displaced water mass

B = (Mwb+2*Mwf+2*Mwc)*9.81; %Buoyant force
W = (Mb+2*Mf+2*Mc)*9.81; %Body weight

%Dc = 0.5*Cdc*rhow*(v^2)*(2*pi*(d/2)*h); %Towed array drag force
%Lc = 0.5*Clc*rhow*(v^2)*(2*pi*(d/2)*h); %Towed array lift force
Dc = 0.5*Cdc*rhow*(v^2)*((d)*h); %Towed array drag force
Lc = 0.5*Clc*rhow*(v^2)*((d)*h); %Towed array lift force
Db = 0.5*Cd*rhow*(v^2)*l*b; %Body drag force
Lb = 0.5*Cl*rhow*(v^2)*w*b; %Body lift force
Lf = 0.5*Clf*rhow*(v^2)*s*c*cos(beta); %Hydrofoil lift force
Df = 0.5*Cdf*rhow*(v^2)*s*c*sin(beta); %hydrofoil drag force
theta = atand((-2*Lc-Lb-2*Lf-B+W)/(Db+2*Dc+2*Df)); %angle between horizontal and T? in deg
T = (2*Dc+Db+2*Df)/cosd(theta);

%theta = atand((-2*Lc-Lb-B+W)/(Db+2*Dc)); %angle between horizontal and T? in deg
%T = (2*Dc+Db)/cosd(theta);

%A(v) = (sind(k)*(2*Dc*lc-2*Dc*yk-2*Lc*bc+2*Lc*xk-Db*yk+Lb*xk-2*Df*yk-2*Df*lf+2*Lf*xk-2*Lf*bf-T*cosd(theta)*lt+T*cosd(theta)*yk-T*sind(theta)*xk+T*sind(theta)*bt)+cosd(k)*(2*Lc*lc-2*Lc*yk+2*Dc*bc-2*Dc*xk-Lb*yk-Db*xk-2*Lf*yk-2*Lf*lf-2*Df*xk+2*Df*bf+T*sind(theta)*lt-T*sind(theta)*yk+T*cosd(theta)*xk-T*cosd(theta)*bt))/I; %with fins
%A(v) = (sind(k)*(2*Dc*lc-2*Dc*yk-2*Lc*bc+2*Lc*xk-Db*yk+Lb*xk-T*cosd(theta)*lt+T*cosd(theta)*yk-T*sind(theta)*xk+T*sind(theta)*bt)+cosd(k)*(2*Lc*lc-2*Lc*yk+2*Dc*bc-2*Dc*xk-Lb*yk-Db*xk+T*sind(theta)*lt-T*sind(theta)*yk+T*cosd(theta)*xk-T*cosd(theta)*bt))/I; %without fins
%A(v) = (sind(k)*(2*Dc*lc-2*Dc*yk-2*Lc*bc+2*Lc*xk-Db*yk+Lb*xk-2*Df*yk-2*Df*lf+2*Lf*xk-2*Lf*bf)+cosd(k)*(2*Lc*lc-2*Lc*yk+2*Dc*bc-2*Dc*xk-Lb*yk-Db*xk-2*Lf*yk-2*Lf*lf-2*Df*xk+2*Df*bf))/I; %with fins without T
%A(v) = (sind(k)*(2*Dc*lc-2*Dc*yk-2*Lc*bc+2*Lc*xk-Db*yk+Lb*xk)+cosd(k)*(2*Lc*lc-2*Lc*yk+2*Dc*bc-2*Dc*xk-Lb*yk-Db*xk))/I; %without fins without T
%A(s) = (sind(k)*(2*Dc*lc-2*Lc*bc-2*Df*lf-2*Lf*bf) + cosd(k)*(2*Lc*lc+2*Dc*bc-2*Lf*lf+2*Df*bf))/I; %with fins
%A(v) = (sind(k)*(2*Dc*lc-2*Lc*bc) + cosd(k)*(2*Lc*lc+2*Dc*bc))/I; %without fins
%A(v) = (sind(k)*(2*Dc*lc-2*Lc*bc-2*Df*lf-2*Lf*bf-T*cosd(theta)*lt-T*sind(theta)*bt) + cosd(k)*(2*Lc*lc+2*Dc*bc-2*Lf*lf+2*Df*bf+T*sind(theta)*lt-T*cosd(theta)*bt))/I; %with fins
%A(v) = (sind(k)*(2*Dc*lc-2*Lc*bc-T*cosd(theta)*lt-T*sind(theta)*bt) + cosd(k)*(2*Lc*lc+2*Dc*bc+T*sind(theta)*lt-T*cosd(theta)*bt))/I; %without fins
A(v) = ( Lc*lc+Dc*bc-Lf*lf-Df*bf-Lb*lb-Db*bb+T*sind(theta)*lt+T*cosd(theta)*bt+B*lB); %with fins
%A(v) = ( Lc*lc+Dc*bc-Lb*lb-Db*bb+T*sind(theta)*lt+T*cosd(theta)*bt+B*lB); %without fins



v = linspace(10,30);
plot(v, A(v)); 
grid on;
xlabel('Towed array force');  
ylabel('Variation of A');

It shows the following error:

Error using sym/subsindex

Invalid indexing or function definition. Indexing must follow MATLAB indexing. Function arguments must be symbolic variables, and function body must be sym expression.

Error in Initial_tilt (line 92)

A(v) = ( Lc*lc+Dc*bc-Lf*lf-Df*bf-Lb*lb-Db*bb+T*sind(theta)*lt+T*cosd(theta)*bt+B*lB); %with fins

Related documentation

It shows the quantity A to be a double and not a sym function.

Can someone please provide any help regarding this?

Thanks in advance

Answer 1

[Aditya Jha]

Hi!

Please refer to the following MATLAB Answers post with a similar query where function body must be a sym : https://www.mathworks.com/matlabcentral/answers/576544-error-using-sym-subsindex