isAlways: what did I do wrong?

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Art 2012-11-6

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https://ww2.mathworks.cn/matlabcentral/answers/52881-isalways-what-did-i-do-wrong

Hi,

I have a somewhat complicate function of only 1 variable. When I plot it from the range [1, 10], it's clear that the function is always negative. However, when I use isAlways (with appropriate assumptions on the domain of the function), it gives me an unknown (unable to prove). Please find the sample code below. Seems like you'd need R2012 for assumeAlso to work.

Thanks a lot!

clear;
syms x real
W2 = 2*((25*(3*x - 30))/(11*(25*x - 8)^2) - 3/(11*(25*x - 8)) + 75/(25*x - 8)^2)*((3*x - 30)/(11*(25*x - 8)) + 3/(25*x - 8) - 1/11) - 2*((25*(3*x - 27))/(11*(25*x + 17)^2) - 3/(11*(25*x + 17)))*((3*x - 27)/(11*(25*x + 17)) - 1/11);
assumeAlso(x >= 1);
assumeAlso(x < 10);
fW2 = inline(char(W2));
fplot(fW2, [1, 10]);
isAlways(W2 < 0, 'Unknown', 'error');