error using solve function
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hi,
I use the function solve to determine a variable as follows:
x = solve (cos (x) * sin (y) * cos (z) + sin (Z) = 1 ',' x ')
then I evaluated x in terms of y and z, when I replace x by the value finding the equation is not = 1!!
how can i resolve it?
回答（1 个）
Walter Roberson
2015-5-13
Are x and y and z symbolic at the time you call solve? Or are y and z numeric?
If they are symbolic and you later substitute in numeric y and z to the solve() response get a numeric x, and then substitute the numeric x, y, and z into the cos (x) * sin (y) * cos (z) + sin (Z) formula, then you could get something other than 1 due to round-off error.
Also, if your y and z are square matrices of numeric values, then cos (x) * sin (y) * cos (z) would succeed but what not be what you want: you would need to evaluate
cos(x) .* sin(y) .* cos(z)
Notice the ".*" instead of "*" if you are working with vectors or matrices.
4 个评论
Walter Roberson
2015-5-13
When you do the numeric verification, if you are testing with vectors of values, then you will need to use .* vectorization when you write the formulas. Or you could use matlabFunction() on the symbolic expression as that will automatically vectorize.
If you are doing symbolic verification instead of numeric, and you do not get 1, then you might need to simplify() the result.
Torsten
2015-5-22
I'd be interested what you get for x after applying "solve".
Best wishes
Torsten.
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