constraints

问题 I am trying to to solve ODEs restricted to positive solutions, i.e.: dx/dt=f(x) with x>=0 . In MATLAB this is very easy to implement. Is there any workaround or package for R to restrict the solution-space to positive values only? This is very crucial in my case and unfortunately there is no alternative. I searched for a while now but without any success. :-( 回答1: There's still not quite enough to go on here. For the sorts of problems I'm familiar with, modifying the system to operate on the

问题 I just began learning Constraint Layout and it's pretty cool, I have come to topic ConstraintSet and got stuck. I have seen an example of ConstraintSet in developer documentation but I am not able to get the idea, I have implemented the code as it is and it's working but I am really unclear about the concept. How constraints work in different ConstraintSet is all I want to know about. Here is what i have done: activity_main.xml <?xml version="1.0" encoding="utf-8"?> <android.support

问题 I'm updating a very large number of objects in batches and want to ignore any duplicates. What is the best way of doing this? My understanding is that if a ConstrainViolationException is thrown all the other objects in the batch will NOT be persisted. 回答1: This was my solution: private void saveBatch() { StatelessSession session = sessionFactory.openStatelessSession(); Transaction tx = session.beginTransaction(); try { for (Object t : batchList) { session.insert(t); } tx.commit(); } catch

问题 I have a SQL 2005 table with millions of rows in it that is being hit by users all day and night. This table is referenced by 20 or so other tables that have foreign key constraints. What I am needing to do on a regular basis is delete all records from this table where the "Active" field is set to false AND there are no other records in any of the child tables that reference the parent record. What is the most efficient way of doing this short of trying to delete each one at a time and

问题 I have table say table1 with a colum say checkColumn, now I want to put a check constraint to the field checkColumn which would allow only data which is there in another table say table 2 for some conditions, I tried this like this, ALTER TABLE table1 ADD CHECK (checkColumn=(select field1 from table2 where field2='ABC') ) //the select is not scalar but as I realized it doesn't allow sub-query string in the check condition,I searched a little and read I should use a foreign key,or trigger, or

问题 Can anyone give a clear explain of these 3 concept? What's the difference and how to use them? 回答1: size hint is the preferred size of the widget, layouts will try to keep it as close to this as possible. size policy describes how the size may change when the preferred size cannot be used (can it stretch or shrink) see the QSizePolicy::Policy enum for a description of each. size constraint are the maximumSize and minimumSize the widget can be. 来源： https://stackoverflow.com/questions/20327855

问题 I have a list of items I want to buy. The items are offered by different shops and different prices. The shops have individual delivery costs. I'm looking for an optimal shopping strategy (and a java library supporting it) to purchase all of the items with a minimal total price. Example: Item1 is offered at Shop1 for $100, at Shop2 for $111. Item2 is offered at Shop1 for $90, at Shop2 for $85. Delivery cost of Shop1: $10 if total order < $150; $0 otherwise Delivery cost of Shop2: $5 if total

问题 This view is not constrained, it only has designtime positions, so it will jump to (0,0) unless you add constraints. The layout editor allows you to place widgets anywhere on the canvas, and it records the current position with designtime attributes (such as layout_editor_absoluteX.) These attributes are not applied at runtime, so if you push your layout on a device, the widgets may appear in a different location than shown in the editor. To fix this, make sure a widget has both horizontal

问题 I have a table with a column that contains a few null values. I want to add a NOT NULL constraint on that column without updating the existing nulls to a non-null value. I want to keep the existing null values and check for future rows that they contain a not null value for this column. Is this possible? How? 回答1: You can add an unvalidated constraint - it will not look at existing rows, but it will be checked for any new or updated rows. ALTER TABLE mytable MODIFY mycolumn NOT NULL

问题 I am trying to programmatically set the constraint for a multiplier in swift, and when I set the value, it just gives me the error, "Cannot assign to the result of this expression"... I declared the NSLayoutConstraint with an IBOutlet, and then set the multiplier, same as I did with the constant for another, which works fine, but this one won't accept it... @IBOutlet weak var clockWidthConstraint: NSLayoutConstraint! override func updateViewConstraints() { super.updateViewConstraints()