if x is a variable, solve for x

Question

Kyle Langford 2021-4-8

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/795872-if-x-is-a-variable-solve-for-x

编辑： Adam Danz 2021-4-8

I am open to any better ways of doing this. I am brand new to Matlab.

What I am trying to do is write a code to solve kinematic equations, and if the user inputs one of the prompts as a variable, then display the correlating variable. Example:

When promted

what is your x value? x %user inputs a variable as itself

what is your x_0 value? 0

what is your v_0 value? 5

what is your t value? 10

Final distance = 50

for any of the given options.

Hopefully this makes sense.

syms x x_0 v_0 t
equation = x==x_0+v_0*t
x= input('What is your x value?');
x_0 = input('What is your x_0 value?');
v_0 = input('What is your v_0 value?');
t = input('What is your t value?');
equation = x==x_0+v_0*t;
S=solve(equation,"IgnoreProperties",true);
if x==x
    fprintf('Distance is %d\n', S)
else
    ;
end
if x_0==x_0
    fprintf('Initial Distance is %d\n', S)
else
    ;
end
if v_0==v_0
    fprintf('Initial Velocity is %d\n', S)
else
    ;
end
if t==t
    fprintf('Time is %d\n', S)
else
    ;
end

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Answer 1

Walter Roberson 2021-4-8

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/795872-if-x-is-a-variable-solve-for-x#answer_669937

在 MATLAB Online 中打开

If the user inputs a variable name for exactly one of the prompts, then symvar(equation) will tell you which variable it was.

solving_for = symvar(equation);
switch solving_for
    case sym('x')
        name = 'Distance';
    case sym('x_0')
        name = 'Initial Distance';
    case sym('v_0')
        name = 'Initial Velocity';
    case sym('t')
        name = 'Time';
    otherwise
        error('wrong variable to solve for');
end
fprintf('%s is %g\n', name, S);