undefined variable error when the variable is there

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Birgitt O'Connor
Birgitt O'Connor 2019-11-14
回答： Star Strider 2019-11-14
my code was working yesterday but now it is telling me I have an undefined variable when the variable is stated. What do I do?
%Cape Cod, Massachusetts
l = 11000; %m length of canal (7 miles/11km)
d = 9.8; %m depth of canal MLLW
rho = 1025; %kg/m^3 seawater density
g = 9.81; %m/s^2 gravity constant
x = [0:100:l];
t = [0 (pi/2) pi (3*pi)/2];
%East
HTEam = 3.11; % m high water at the East on October 29rd, 2019
LTEam = -0.30;
%military time
HTEtam = 0018;% military time of high water at the East on October 29rd, 2019
LTEtam = 0622;
HTEtpm = 1236;
LTEtpm = 1855;
TE = (HTEtpm-HTEtam);
fprintf('East tidal period = %1.0f (military time) \n',TE)
TEs = (12*60*60)+(18*60); %tidal period converted to seconds
TAE = (HTEam-LTEam)/2;
fprintf('East tidal amplitude = %1.2f m \n',TAE)
%West
HTWam = 1.58; % m time of high water at the West End on October 29rd, 2019
LTWam = -0.091;
% military time
HTWtam = 1029;
LTWtam = 0516;
HTWtpm = 2255;
LTWtpm = 1755;
TW = (HTWtpm-HTWtam);
fprintf('West tidal period = %1.0f (military time) \n',TW)
TWs = (12*60*60)+(26*60); %tidal period converted to seconds
TAW = (HTWam-LTWam)/2;
fprintf('West tidal amplitude = %1.2f m \n',TAW)
fprintf('EAST\n')
LE = TEs*sqrt(g*d);
fprintf('East wavelength = %1.2f m \n',LE)
kE = (2*pi)/LE; %wave number
LoE = (g*TEs^2)/(2*pi);
sigmaE = (2*pi)/TEs;
etaoE = 2*TAE*sin(kE*l);
CoE = LE/TEs; %wave celerity
LW = TWs*sqrt(g*d);
fprintf('West wavelength = %1.2f m \n',LW)
kW = (2*pi)/LW; %wave number
LoW = (g*TWs^2)/(2*pi);
sigmaW = (2*pi)/TWs;
beta = (5*pi)/3;
CoW = LoW/TWs; %wave celerity
etaoW = 2*TAW*sin(kW*(-l));
for i = l:length(t)
for j = l:length(x)
etaE(i,j) = etaoE.*((sin(kE.*(l-x(j))))./(sin(kE.*l))).*cos(t(i)); %surface elevation
uE(i,j) = (etaoE./d).*CoE.*((cos(kE.*(l-x(j))))./sin(kE.*l)).*sin(t(i)); %wave speed
etaW(i,j) = (etaoW.*((sin(kW.*x(j)))./(sin(kW.*l))).*cos(t(i)))+beta; %wave slope
uW(i,j) = -((etaoW./d).*CoW.*((cos(kW.*x(j)))./sin(kW.*l)).*sin(t(i)))+beta; %wave speed
etaT(i,j) = etaE(i,j)+etaW(i,j);
uT(i,j) = uE(i,j)+uW(i,j);
end
end
figure(1)
plot(x,etaT(1,:),'b',x,etaT(2,:),'r',x,etaT(3,:),'g',x,etaT(4,:),'k')
%hold on
%plot ([sb sb], etaT(1,:))
xlabel('l, length of channel (m)')
ylabel('tidal elevation (m)')
title('Tidal Elevation Changes')
legend('t=0','t=pi/2','t=pi','t=3pi/2')
figure(2)
plot(x,uT(1,:),'b',x,uT(2,:),'r',x,uT(3,:),'g',x,uT(4,:),'k')
xlabel('l, length of channel (m)')
ylabel('Current velocity (m/s)')
title('Current velocity over tidal length')
legend('t=0','t=pi/2','t=pi','t=3pi/2')

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采纳的回答

Star Strider
Star Strider 2019-11-14
Please note that:
l ~= 1
You typed:
for i = l:length(t)
for j = l:length(x)
however I believe you intended:
for i = 1:length(t)
for j = 1:length(x)
Since ‘l’ is 1.1E+4, the loops are immediately satisfied using ‘l’ as an initial value for them, and so never iterate.

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