Matlab程序错误，跪求高手解答

错误提示如下：???Undefinedfunctionorvariable'ROOTDIR'.Errorin==>realField1phExampleat29grdec... 错误提示如下：
??? Undefined function or variable 'ROOTDIR'.

Error in ==> realField1phExample at 29
grdecl = fullfile(ROOTDIR, 'examples', 'grids', 'GSmodel.grdecl');

出错的程序源码如下：

%% Pressure Solver: Example of a Real Field Model
% In the example, we will solve the single-phase pressure equation
%
% $$\nabla\cdot v = q, \qquad v=\textbf{--}\frac{K}{\mu}\nabla p,$$
%
% using the corner-point geometry from a real North Sea field.
%
% <html>
% The purpose of this example is to demonstrate how the mimetic flow solver
% can be applied to compute flow on a real grid model that has degenerate
% cell geometries and non-neighbouring connections arising from a large
% number of faults, eroded layers, pinch-outs, and inactive cells. A more
% thorough examination of the model is given in a
% <a href="../../grids/html/realFieldModelExample.html">separate example</a>.
% </html>
%
% For confidentiallity reasons, we will not use real data for rock
% parameters and well paths. Instead, synthetic permeability data are
% generated by (make-believe) geostatistics and vertical wells are placed
% quite haphazardly throughout the domain.
%
% <html>
% Experimentation with this model is continued in <a
% href="../../2ph/html/realField2phExample.html">
% another example</a>, in which we solve a simplified two-phase model.
% </html>

%% Check for existence of input model data
grdecl = fullfile(ROOTDIR, 'examples', 'grids', 'GSmodel.grdecl');
if ~exist(grdecl, 'file'),
error('Model data is not available.')
end

%% Read and process the model
% We start by reading the model from a file in the Eclipse formate
% (GRDECL). As shown in <realFieldModelExample.html the more thorough
% discussion>, the model has two components, of which we will only use the
% first one.
grdecl = readGRDECL(grdecl);
G = processGRDECL(grdecl); clear grdecl;
G = computeGeometry(G(1));

%% Set rock and fluid data
% The permeability is lognormal and isotropic within nine distinct layers
% and is generated using our simplified 'geostatistics' function and then
% transformed to lay in the interval 200-2000 mD. The single fluid has
% density 1000 kg/m^3 and viscosity 1 cP.
gravity off
K = logNormLayers(G.cartDims, rand(9,1), 'sigma', 1.5);
K = 200 + (K-min(K))/(max(K)-min(K))*1800;
rock.perm = convertFrom(K(G.cells.indexMap), milli*darcy); clear K;
fluid = initSingleFluid('mu' , 1*centi*poise , ...
'rho', 1000*kilogram/meter^3);

clf,
plotCellData(G,log10(rock.perm),'EdgeColor','k');
axis off, view(15,60), h=colorbar('horiz'); zoom(2.5),
cs = [200 400 700 1000 1500 2000];
caxis(log10([min(cs) max(cs)]*milli*darcy));
set(h, 'XTick', log10(cs*milli*darcy), 'XTickLabel', num2str(round(cs)'));
以上只是出错的代码，后面的代码没有附上来，哪位高手帮帮我，问题解决之后我再加分，谢谢
第二十九行：grdecl = fullfile(ROOTDIR, 'examples', 'grids', 'GSmodel.grdecl');
，matlab有没有“ROOTDIR”命令？另外，我要打开的数据文件的路径如下：D:\matlab\mrst-2010a\mrst-2010a\examples\grids\GSmodel.grdecl。我的问题可能没有描述清楚，朋友也可以加我QQ好友675622075，再次谢过展开

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