Gradient function
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From: Rupika Bandara on 3 Apr 2010 08:46 I want to get second derivative of mode shape of a pin supported beam. I have deflection values corresponding to beam length. I do not know the function of the mode shape. Total length of beam is 2.4m. mode shape value is y. x=[0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4] y=(-0.000230888 0.167612145 0.355166168 0.497419808 0.54998773 0.497419808 0.355166168 0.167612145 -0.000230888) How can I find the second derivative of this curve?
From: John D'Errico on 3 Apr 2010 08:56 "Rupika Bandara" <rupika23(a)yahoo.com> wrote in message <hp7dae$omi$1(a)fred.mathworks.com>... > I want to get second derivative of mode shape of a pin supported beam. I have deflection values corresponding to beam length. I do not know the function of the mode shape. Total length of beam is 2.4m. mode shape value is y. > x=[0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4] > y=(-0.000230888 0.167612145 0.355166168 0.497419808 0.54998773 0.497419808 0.355166168 0.167612145 -0.000230888) > How can I find the second derivative of this curve? Interpolate with a spline, then differentiate the spline. Or model it with a LOW order polynomial, then differentiate. John
From: Rupika Bandara on 4 Apr 2010 23:19 "John D'Errico" <woodchips(a)rochester.rr.com> wrote in message <hp7dt4$2qi$1(a)fred.mathworks.com>... > "Rupika Bandara" <rupika23(a)yahoo.com> wrote in message <hp7dae$omi$1(a)fred.mathworks.com>... > > I want to get second derivative of mode shape of a pin supported beam. I have deflection values corresponding to beam length. I do not know the function of the mode shape. Total length of beam is 2.4m. mode shape value is y. > > x=[0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4] > > y=(-0.000230888 0.167612145 0.355166168 0.497419808 0.54998773 0.497419808 0.355166168 0.167612145 -0.000230888) > > How can I find the second derivative of this curve? > > Interpolate with a spline, then differentiate the spline. > Or model it with a LOW order polynomial, then differentiate. > > John Hi John, I do not know how to interpolate with a spline. Can you please explain me using an example? Please help me. This is urgent. Rupika
From: TideMan on 4 Apr 2010 23:34 On Apr 5, 3:19 pm, "Rupika Bandara" <rupik...(a)yahoo.com> wrote: > "John D'Errico" <woodch...(a)rochester.rr.com> wrote in message <hp7dt4$2q....(a)fred.mathworks.com>... > > "Rupika Bandara" <rupik...(a)yahoo.com> wrote in message <hp7dae$om...(a)fred.mathworks.com>... > > > I want to get second derivative of mode shape of a pin supported beam.. I have deflection values corresponding to beam length. I do not know the function of the mode shape. Total length of beam is 2.4m. mode shape value is y. > > > x=[0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4] > > > y=(-0.000230888 0.167612145 0.355166168 0.497419808 0.54998773 0.497419808 0.355166168 0.167612145 -0.000230888) > > > How can I find the second derivative of this curve? > > > Interpolate with a spline, then differentiate the spline. > > Or model it with a LOW order polynomial, then differentiate. > > > John > > Hi John, > I do not know how to interpolate with a spline. Can you please explain me using an example? Please help me. This is urgent. > Rupika Urgent? Humpf............ Lack of planning on your part DOES NOT constitute an emergency on ours. For splines: help interp1
From: Rupika Bandara on 5 Apr 2010 05:00 TideMan <mulgor(a)gmail.com> wrote in message <b95e7444-c62c-4f66-a905-60cfe75e5df7(a)x3g2000yqd.googlegroups.com>... > On Apr 5, 3:19 pm, "Rupika Bandara" <rupik...(a)yahoo.com> wrote: > > "John D'Errico" <woodch...(a)rochester.rr.com> wrote in message <hp7dt4$2q...(a)fred.mathworks.com>... > > > "Rupika Bandara" <rupik...(a)yahoo.com> wrote in message <hp7dae$om...(a)fred.mathworks.com>... > > > > I want to get second derivative of mode shape of a pin supported beam. I have deflection values corresponding to beam length. I do not know the function of the mode shape. Total length of beam is 2.4m. mode shape value is y. > > > > x=[0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4] > > > > y=(-0.000230888 0.167612145 0.355166168 0.497419808 0.54998773 0.497419808 0.355166168 0.167612145 -0.000230888) > > > > How can I find the second derivative of this curve? > > > > > Interpolate with a spline, then differentiate the spline. > > > Or model it with a LOW order polynomial, then differentiate. > > > > > John > > > > Hi John, > > I do not know how to interpolate with a spline. Can you please explain me using an example? Please help me. This is urgent. > > Rupika > > Urgent? Humpf............ > Lack of planning on your part DOES NOT constitute an emergency on > ours. > > For splines: > help interp1 Hi John, Thank you very much for your help. I interpolated with a spline. This is the method I used x=[0:0.3:2.4] y=(-0.000230888 0.167612145 0.355166168 0.497419808 0.54998773 0.497419808 0.355166168 0.167612145 -0.000230888) xi=[0:0.3:2.4] yi = interp1(x,y,xi,'spline') firstder=diff(yi) seconder=diff(firstder) I used same point as x for xi also. As I want second derivative only at 7 points. Is this right? I checked it with xi=[0:0.15:2.4] also. But it gave very different values compared to first method. Please help me to clarify this. Rupika
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