"If else" statements

Question

EnjoyLife 2020-11-8

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/640640-if-else-statements

回答： Image Analyst 2020-11-8

How to do the if else statement for the [X] below because my coding keeps showing error at line 32? Can someone help me in this? Thank you vey much.

%Base
base='What is the volume flowrate of base (L/h)?';
V_base=input(base) %volume flowrate of base (L/h)
base_pH='what is the pH of the base?'
pH_base=input(base_pH) %base pH
C_base_H=10^-pH_base; % conc of H+ in base (mol/L)
C_base_OH=10^(-14+pH_base); %conc of OH- in base (mol/h)
x_base=C_base_OH-C_base_H; 
%acid
acid='what is the volume flowrate of acid (L/h)?'
V_acid=input(acid) %volume flowrate of acid (L/h)
acid_pH='What is the pH of the acid?'
pH_acid=input(acid_pH) %acid pH
C_acid_H=10^-pH_acid; % conc of H+ in acid (mol/L)
C_acid_OH=10^(-14+pH_acid); %conc of OH- in acid (mol/h)
x_acid=C_acid_OH-C_acid_H;
V=4000; %volume CSTR (L)
syms x(t)
ode=diff(x,t)==(V_base*x_base+V_acid*x_acid-(V_acid+V_base)*x)/V;
cond=x(0)==0;
 
xSol(t)=dsolve(ode,cond);
t=[1:60]; % time, hour
[X]=[xSol(t)];
if [X]>0
    [pH]=-log((X/2)+sqrt(1+((4*10^-14)/X.^2))-1);
elseif [X]<0
    [pH]=-log((-X/2)+sqrt(1+((4*10^-14)/X.^2))+1);
else [X]=0
    [pH]=-log(sqrt(10^-14));
end   
figure
plot(t,pH)
title('pH over time in CSTR')
xlabel('time,hour')
ylabel('pH of outlet stream')

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Answer 1

Image Analyst 2020-11-8

0
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/640640-if-else-statements#answer_538030

在 MATLAB Online 中打开

I don't have the symbolic toolbox so I can't run it, but one error I see right off the bat is that you're not using a doubl equals

else [X]=0

should be

else X == 0

Additionally, you don't need square brackets around variables.

And if X is a multi-element array, you'll need to use any(X) or all(X) depending if you want to go in there if 1 or more values are 0, or if you need all values to be zero.