Develop Reference

java.math.BigDecimal.scale() equivalent for double

I've got a matrix of values like the one below that I need to scale. I've been looking around for an inbuilt function if there is one that could do this for me. I haven't found one & so have ended up writing code to do the scaling using the below formula
scaledMatrix = (Matrix - MeanMatrix)/Standard Deviation
This code is a bit buggy & I'm working on correcting it. While I do that, I happened to bump on java.math.BigDecimal.scale() & did look up an equivalent for double as the matrix I have is double type numbers
If someone could please help me with details on
1) If there is an inbuilt function that accepts matrix of values & returns me the scaled matrix
2) `java.math.BigDecimal.scale()` equivalent for `double` type data
Any help would be much appreciated please.

The BigDecimal.scale() method does not do what you seem to think it is doing. A BigDecimal value is stored as a * 10^b (where ^ denotes exponentiation). The BigDecimal.scale() method basically returns the b part of that.
I do not know of a similar method for double values, nor do I know of a method which performs the function you need. Since you put apache-commons in the tags, I suggest you look into Apache Commons's extensive statistical library.

Validation of a geometry in WKT format

I am new to GIS area and I need to validate a geometry in WKT format in java, to check whether a simple polygon is a closed loop, i.e the start and end points of the vertices should be the same. I am currently using jGeometry class of oracle spatial(com.oracle.sdoapi), get the first and last vertices and comparing them. also, i am using getType() method to check whether it is a simple polygon or not. The following is the piece of code that am using:
WKT wkt = new WKT();
JGeometry geometry = wkt.toJGeometry(wkt.getBytes());
double[] d1 = geometry.getFirstPoint();
double[] d2 = geometry.getLastPoint();
if(!jGeometry.getType() == jGeometry.GTYPE_POLYGON){
//error message for other geometries
}
Is there any simple way of doing this or is there any API available? I dont want to reinvent the wheel, if it is already done and simple to use. Thanks!

The Java Topology Suite contains a WKTReader class that will suit your purposes. See http://tsusiatsoftware.net/jts/javadoc/com/vividsolutions/jts/io/WKTReader.html. You can use WKTReader to parse the WKT, and look for ParseExceptions, which indicate an invalid WKT.
If the WKT parses, you can then use the instanceof operator or WKTReader.getGeometryType() to determine the type of parsed Geometry class, and see if it's one of the Geometry types (Polygon or Multipolygon) with closed shells like Polygon or Multipolygon.

MATLAB: Java String[] conversion

I'm quite new to MATLAB programming and I ran into some trouble:
I want to call a dSPACE MLIB libriary function. According to their samples, it requires a string array as argument:
variables = {'Model Root/Spring-Mass-Damper System/Out1';...
'Model Root/Signal\nGenerator/Out1'};
libFunction(variables);
This variables is passed to the function. My problem is now: I have a frontend application where the user can choose from an arbitary number of strings which should be passed to the matlab function. Since the frontend is writtten in Java, the type of the incoming data is java.lang.String[].
How can I convert an array of java strings to something with the same type as the sample variable above (I think it is a cell array of cell arrays or sth like that).
Thanks in advance!

Take a look at the documentation. MATLAB makes it very easy to convert to and from Java types.
Handling data returned from Java
Dealing with Java arrays
You can convert an array of Java strings to either a cell or char array in MATLAB. Using cell arrays can work even with jagged arrays (which are permitted in Java).
Here are two simple examples:
%# Preparing a java.lang.String[] to play with.
a = javaArray('java.lang.String',10);
b = {'I','am','the','very','model','of','a','modern','major','general'};
for i=1:10; a(i) = java.lang.String(b{i}); end;
%# To cell array of strings. Simple, eh?
c = cell(a);
%# To char array. Also simple.
c = char(a);

reading data from Matlab into Java

I'm trying to read a matrix produced in Matlab into a 2D array in java.
I've been using jmatio so far for writing from java to a .mat file (successfully), but now can't manage to go the other way around.
I've managed to import a matrix into an MLArray object using this code:
matfilereader = new MatFileReader("filename.mat");
MLArray j = matfilereader.getMLArray("dataname");
But other than getting its string representation I couldn't manage to access the data itself. I found no example for this or documentation on the library itself, and I actually wrote a function to parse the intire string into a double[][] array but that's only good if the matrix is smaller than 1000 items...
Would be grateful for any experience or tips,
thanks,
Amir

matfilereader.getMLArray has several subclasses to access different kinds of data in MLArray object.
To represent double array you can cast MLArray to MLDouble:
MLDouble j = (MLDouble)matfilereader.getMLArray("dataname");

I'm not familiar with that tool, but it's pretty old. Try saving to an older version of *.mat file and see if your results change. That is, add either the '-v7.0' or '-v6' flag when you save you r*.mat file.
Example code:
save filename var1 var2 -v7.0
or
save filename var1 var2 -v6

Is there a Java equivalent of Python's printf hash replacement?

Specifically I am converting a python script into a java helper method. Here is a snippet (slightly modified for simplicity).
# hash of values
vals = {}
vals['a'] = 'a'
vals['b'] = 'b'
vals['1'] = 1
output = sys.stdout
file = open(filename).read()
print >>output, file % vals,
So in the file there are %(a), %(b), %(1) etc that I want substituted with the hash keys. I perused the API but couldn't find anything. Did I miss it or does something like this not exist in the Java API?

You can't do this directly without some additional templating library. I recommend StringTemplate. Very lightweight, easy to use, and very optimized and robust.

I doubt you'll find a pure Java solution that'll do exactly what you want out of the box.
With this in mind, the best answer depends on the complexity and variety of Python formatting strings that appear in your file:
If they're simple and not varied, the easiest way might be to code something up yourself.
If the opposite is true, one way to get the result you want with little work is by embedding Jython into your Java program. This will enable you to use Python's string formatting operator (%) directly. What's more, you'll be able to give it a Java Map as if it were a Python dictionary (vals in your code).