How to do the matrix calculations

Dear all, Here is the question. I have two matrices named Matrix A(temperature data) and Matrix B(salinity data). I wanna calculate Matrix C(density data), and we know C(density) is a function of A(temperature) and B(salinity). And I hope to plot the figure, for which, density variations with the time. Best regards, Mingda

[Image Analyst]

Where is the question? You didn't actually ask one. All we know is that you have the (badly-named) matrices A and B and you want to calculate C. You didn't give us the formula to compute C based on A and B so I guess you know that. I don't know if you already have C and need to find out the function of A and B, OR you already know the function and just want to find out the best way to apply the function to generate C. And I'm sure you know about the plot() function so I'm not sure what "plot the figure" means. I'm sure you know how you could plot temp5, temp6, ...salinity4, or salinity 5 with the plot() function. But I don't know what "figure" you're talking about and how a "figure" could be plotted. A figure is a GUI that has various controls on it like buttons, axes, scrollbars, etc. What do you mean you want to plot that?

Try these links: http://www.mathworks.com/matlabcentral/answers/6200-tutorial-how-to-ask-a-question-on-answers-and-get-a-fast-answer and http://www.mathworks.com/matlabcentral/answers/728-how-do-i-write-a-good-question-for-matlab-answers

[Mingda Wang]

Sorry, I did not make it clear, the formula is like this

     rho_0 = 999.842594+6.793952e-2*T-9.095290e-3*T.^2+...
        1.001685e-4*T.^3-1.120083e-6*T.^4+6.536335e-9*T.^5;
    % --eqn (2):
    A = 8.24493e-1-4.0899e-3*T+7.6438e-5*T.^2-8.2467e-7*T.^3+5.3875e-9*T.^4;
    % --eqn (3):
    B = -5.72466e-3+1.0227e-4*T-1.6546e-6*T.^2;
    % --eqn (4):
    C = 4.8314e-4;
    % --eqn (5):
    rho = rho_0+A.*S+B.*S.^(3/2)+C.*S;

source code (https://github.com/GLEON/Lake-Analyzer/blob/master/Source/waterDensity.m)

and I have already got A and B and the formula C=fx(A,B),wanna the C result

[Amit]

The equation you wrote are right and should give you the answer. Isn't rho the solution you want? Are you having trouble exporting the data as vector T for temperature and S for salinity?

Answer 1

[Youssef Khmou]

As you have the formula, you can get C given rho0 and rho are known :

C=(rho-rho0-A*S-B*S^(3/2))*inv(S);

[Mingda Wang]

Hi Youssef, Here, in the formula, C is indeed a constant.However, Matrix C is related to the density (rho).Sorry for the confusion of C and Matrix C.Probably I should use other alphabetic number instead.

[Youssef Khmou]

alright Mingda, so is the problem solved ?

[Mingda Wang]

:( not yet, the values in Matrix A,Matrix B and Matrix C are with correspondence, to be specific, C1=fx(A1,B1),C2=fx(A2,B2).I still could not get access to the calculation of Matrix C

Answer 2

[Mingda Wang]

problem solved by excel