[gradsusr] Trend MAP help!

[Andrew Friedman]

Hi Malcolm,

I believe that what you are doing by plotting trendlast-trendl is comparing the fitted trend line at the last time step minus that of the first time step.
I think that (trendlast-trendl)/ # of time steps should equal the slope. Is that what you find?

Best, Andrew

> On Dec 23, 2015, at 5:11 AM, Malcolm Tang <malct32 at gmail.com> wrote:
> 
> Hi Andrew,
> 
> Thanks for your guidance, it worked wonderfully.
> 
> Just a quick question, though.
> 
> 'sdfopen precipitation.nc'
> 'set lon 0 360'
> 'set lat -90 -75'
> 'set mproj sps'
> 'set t 1 last'
> 
> 'd precipitation'
> 'ltrend precipitation precl slope error'
> 'c'
> 
> 'set t 1'
> 'd precl'
> 'define trend1=precl'
> 
> 'c'
> 'set t last'
> 'd precl'
> 'define trendlast=precl'
> 'c'
> 
> 'd trendlast-trendl'
> 
> *a spatial map comes out*
> 
> Is this the correct way to display the fluctuation of precipitation trend?
> 
> Regards,
> Malcolm
> 
> On Fri, Dec 18, 2015 at 4:59 AM, Andrew Friedman <andfried at gmail.com> wrote:
> Hi Malcolm,
> 
> If you are looking for the slope (the rate of change per time step) you need to add another term when you call trend
> 
> For example:
> 'ltrend prec precl precslope'
> 
> >From the ltrend.gs”
> 
> ga-> ltrend
>   Calculate linear trend over time (based on least-squares fitting).
> 
>   USAGE: ltrend <input> [<output> [<slope> [<rmse>]]]
>     <input>: input field. Can be any GrADS expression.
>     <output>: output field, i.e., fitted trend line. Default=<input>.
>     <slope>: slope of fitted trend line, i.e., change of <input> per time step.
>     <rmse>: root mean square error.
> 
> Andrew
> 
> > On Dec 17, 2015, at 1:28 PM, Malcolm Tang <malct32 at gmail.com> wrote:
> >
> > Hi Andrew,
> > Yes I've set it as
> >
> > "set t 1 last"
> >
> > For your info, I tried this and a spatial map came out:
> >
> > 'set lon 0 360'
> > 'set lat -90 -75'
> > 'set mproj sps'
> > 'set t 1 last'
> >
> > 'd prec'
> >
> > 'ltrend prec precl'
> >
> > 'd precl'
> >
> > I'm not sure if it's the spatial trend map that I'm looking for though....
> >
> > But since the time is set from 1 to last, I can observe that the map actually changes from 1 to the last time step.
> >
> > Any idea or suggestion?
> >
> > Thanks.
> > Malcolm
> >
> >
> > On Thu, Dec 17, 2015 at 5:32 PM, Andrew Friedman <andfried at gmail.com> wrote:
> > Hi Malcolm,
> >
> > In your text earlier, it looks like your time is set to 1. Can you try setting time to varying?
> >
> > Andrew
> >
> > > On Dec 17, 2015, at 3:38 AM, Malcolm Tang <malct32 at gmail.com> wrote:
> > >
> > > Hi Andrew,
> > >
> > > I removed the bracket and ....... nothing came out?
> > >
> > > I typed:
> > >
> > > "ltrend prec fitted trend line" nothing came out.
> > >
> > > "ltrend prec fitted trend line 0.2 0.025" nothing came out.
> > >
> > > Should I be expecting a result or something? Because I'm expecting a spatial map to come up.
> > >
> > > Thanks!
> > > Malcolm
> > >
> > > On Wed, Dec 16, 2015 at 4:05 PM, Andrew Friedman <andfried at gmail.com> wrote:
> > > HI Malcolm,
> > >
> > > You shouldn’t type the brackets - they’re placeholders to indicate optional values.
> > >
> > > Andrew
> > >
> > > > On Dec 16, 2015, at 4:55 AM, Malcolm Tang <malct32 at gmail.com> wrote:
> > > >
> > > > Hi all,
> > > >
> > > > I want to plot the trend map of precipitation in antarctica (75s-90s) from 1999-2015.
> > > >
> > > > I have done some searching and saw someone suggested using BinGuan's script ltrend.gs
> > > > I have copied the script and the dependencies qdims.gsf.
> > > >
> > > > So these are what I type in grads:
> > > >
> > > > 'set lon 0 360'
> > > > 'set lat -90 -75'
> > > > 'set mproj sps'
> > > > 'set t 1'
> > > >
> > > > 'd prec'
> > > > 'ltrend prec [fitted trend line [0.2[0.025]]]'
> > > >
> > > > and there will be error coming out: DEFINE error: Name too long; missing '='
> > > >
> > > > Anyone who has experience with ltrend.gs PLEASEEEEEEE help!!!
> > > >
> > > > Thanks
> > > > Malcolm
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