I am new learner of Mat lab. I want to transfer a big following data from excel into Mat Lab. In Mat lab, I am interested to find polynomial of X (constant) with different values of Y to get polynomial of each. Then I want to double differentiate each polynomial with respect to X and put equal to zero. Then I want to solve this equation to get value of X.  
X: 1    2    3    4    5    6    7    8
Y: 9    8    7    6    5    4    3    2
Y: 7    6    5    4    3    2    1    0.5
Y: 9    7    6    5    4    3    2    1
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In this procedure I am facing following problems.
1-    What should be format of file in importing data into Matlab
2-    I will use coef = Polyfit(x,y,n) to get coefficient of equation. But, in Mat lab, I cannot find differentiation by using coefficient of an equation.
3-    How will I write the loop of program because there are lot of values